diff --git a/docs/technical/mod-package.md b/docs/technical/mod-package.md
index 4c31f69b..6123b28f 100644
--- a/docs/technical/mod-package.md
+++ b/docs/technical/mod-package.md
@@ -413,9 +413,19 @@ when you compile it.
 
 ## Release notes
 ## Upcoming release
+* Migrated from .NET Standard 2.0 to .NET 5.0.  
 * Added detection for Xbox app game folders.
 * Internal refactoring.
 
+**Troubleshooting:**  
+Due to the framework change, you might see build errors like _task failed unexpectedly_ that mentions `System.Runtime Version=5.0.0`. If so:
+
+1. Make sure you have Visual Studio 2022 or later.
+2. Exit all instances of Visual Studio.
+3. Delete the hidden `.vs` folder in your solution folder.
+4. Delete the `bin` and `obj` folders in each project folder.
+5. Reopen the solution and rebuild, and now it should work fine.
+
 ## 4.0.0
 Released 30 November 2021.
 
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/SMAPI.ModBuildConfig.Analyzer.csproj b/src/SMAPI.ModBuildConfig.Analyzer/SMAPI.ModBuildConfig.Analyzer.csproj
index 7ac3277e..69fd3dbd 100644
--- a/src/SMAPI.ModBuildConfig.Analyzer/SMAPI.ModBuildConfig.Analyzer.csproj
+++ b/src/SMAPI.ModBuildConfig.Analyzer/SMAPI.ModBuildConfig.Analyzer.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <RootNamespace>StardewModdingAPI.ModBuildConfig.Analyzer</RootNamespace>
     <Version>3.0.0</Version>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
     <IncludeBuildOutput>false</IncludeBuildOutput>
     <OutputPath>bin</OutputPath>
     <LangVersion>latest</LangVersion>
diff --git a/src/SMAPI.ModBuildConfig/SMAPI.ModBuildConfig.csproj b/src/SMAPI.ModBuildConfig/SMAPI.ModBuildConfig.csproj
index 82eac7f6..8e70293e 100644
--- a/src/SMAPI.ModBuildConfig/SMAPI.ModBuildConfig.csproj
+++ b/src/SMAPI.ModBuildConfig/SMAPI.ModBuildConfig.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <!--build-->
     <RootNamespace>StardewModdingAPI.ModBuildConfig</RootNamespace>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
     <LangVersion>latest</LangVersion>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <SuppressDependenciesWhenPacking>true</SuppressDependenciesWhenPacking>
diff --git a/src/SMAPI.Toolkit.CoreInterfaces/SMAPI.Toolkit.CoreInterfaces.csproj b/src/SMAPI.Toolkit.CoreInterfaces/SMAPI.Toolkit.CoreInterfaces.csproj
index 4c92b4db..d69d53d5 100644
--- a/src/SMAPI.Toolkit.CoreInterfaces/SMAPI.Toolkit.CoreInterfaces.csproj
+++ b/src/SMAPI.Toolkit.CoreInterfaces/SMAPI.Toolkit.CoreInterfaces.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <RootNamespace>StardewModdingAPI</RootNamespace>
     <Description>Provides toolkit interfaces which are available to SMAPI mods.</Description>
-    <TargetFrameworks>net5.0; netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net5.0</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
   </PropertyGroup>
 
diff --git a/src/SMAPI.Toolkit/SMAPI.Toolkit.csproj b/src/SMAPI.Toolkit/SMAPI.Toolkit.csproj
index ec27bf79..6a8c4c43 100644
--- a/src/SMAPI.Toolkit/SMAPI.Toolkit.csproj
+++ b/src/SMAPI.Toolkit/SMAPI.Toolkit.csproj
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <RootNamespace>StardewModdingAPI.Toolkit</RootNamespace>
     <Description>A library which encapsulates mod-handling logic for mod managers and tools. Not intended for use by mods.</Description>
-    <TargetFrameworks>net5.0; netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net5.0</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
   </PropertyGroup>
 
diff --git a/src/SMAPI.Toolkit/SemanticVersion.cs b/src/SMAPI.Toolkit/SemanticVersion.cs
index cea8c447..ca9d15f5 100644
--- a/src/SMAPI.Toolkit/SemanticVersion.cs
+++ b/src/SMAPI.Toolkit/SemanticVersion.cs
@@ -198,12 +198,7 @@ namespace StardewModdingAPI.Toolkit
         /// <param name="version">The version string.</param>
         /// <param name="parsed">The parsed representation.</param>
         /// <returns>Returns whether parsing the version succeeded.</returns>
-        public static bool TryParse(string? version,
-#if NET5_0_OR_GREATER
-            [NotNullWhen(true)]
-#endif
-            out ISemanticVersion? parsed
-        )
+        public static bool TryParse(string? version, [NotNullWhen(true)] out ISemanticVersion? parsed)
         {
             return SemanticVersion.TryParse(version, allowNonStandard: false, out parsed);
         }
@@ -213,12 +208,7 @@ namespace StardewModdingAPI.Toolkit
         /// <param name="allowNonStandard">Whether to allow non-standard extensions to semantic versioning.</param>
         /// <param name="parsed">The parsed representation.</param>
         /// <returns>Returns whether parsing the version succeeded.</returns>
-        public static bool TryParse(string? version, bool allowNonStandard,
-#if NET5_0_OR_GREATER
-            [NotNullWhen(true)]
-#endif
-            out ISemanticVersion? parsed
-        )
+        public static bool TryParse(string? version, bool allowNonStandard, [NotNullWhen(true)] out ISemanticVersion? parsed)
         {
             if (version == null)
             {
diff --git a/src/SMAPI.Toolkit/Serialization/Models/Manifest.cs b/src/SMAPI.Toolkit/Serialization/Models/Manifest.cs
index 01010602..3ab5edfb 100644
--- a/src/SMAPI.Toolkit/Serialization/Models/Manifest.cs
+++ b/src/SMAPI.Toolkit/Serialization/Models/Manifest.cs
@@ -115,9 +115,7 @@ namespace StardewModdingAPI.Toolkit.Serialization.Models
         *********/
         /// <summary>Normalize whitespace in a raw string.</summary>
         /// <param name="input">The input to strip.</param>
-#if NET5_0_OR_GREATER
         [return: NotNullIfNotNull("input")]
-#endif
         private string? NormalizeWhitespace(string? input)
         {
             return input
diff --git a/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs b/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs
index f7dc8aa8..dcdbcf74 100644
--- a/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs
+++ b/src/SMAPI.Toolkit/Serialization/Models/ManifestContentPackFor.cs
@@ -33,9 +33,7 @@ namespace StardewModdingAPI.Toolkit.Serialization.Models
         *********/
         /// <summary>Normalize whitespace in a raw string.</summary>
         /// <param name="input">The input to strip.</param>
-#if NET5_0_OR_GREATER
         [return: NotNullIfNotNull("input")]
-#endif
         private string? NormalizeWhitespace(string? input)
         {
             return input?.Trim();
diff --git a/src/SMAPI.Toolkit/Serialization/Models/ManifestDependency.cs b/src/SMAPI.Toolkit/Serialization/Models/ManifestDependency.cs
index e7acf71d..64725818 100644
--- a/src/SMAPI.Toolkit/Serialization/Models/ManifestDependency.cs
+++ b/src/SMAPI.Toolkit/Serialization/Models/ManifestDependency.cs
@@ -54,9 +54,7 @@ namespace StardewModdingAPI.Toolkit.Serialization.Models
         *********/
         /// <summary>Normalize whitespace in a raw string.</summary>
         /// <param name="input">The input to strip.</param>
-#if NET5_0_OR_GREATER
         [return: NotNullIfNotNull("input")]
-#endif
         private string? NormalizeWhitespace(string? input)
         {
             return input?.Trim();
diff --git a/src/SMAPI.Toolkit/Utilities/PathUtilities.cs b/src/SMAPI.Toolkit/Utilities/PathUtilities.cs
index 9a0e2ea7..d035d4cd 100644
--- a/src/SMAPI.Toolkit/Utilities/PathUtilities.cs
+++ b/src/SMAPI.Toolkit/Utilities/PathUtilities.cs
@@ -92,43 +92,7 @@ namespace StardewModdingAPI.Toolkit.Utilities
         [Pure]
         public static string GetRelativePath(string sourceDir, string targetPath)
         {
-#if NET5_0
             return Path.GetRelativePath(sourceDir, targetPath);
-#else
-            // NOTE:
-            // this is a heuristic implementation that works in the cases SMAPI needs it for, but it
-            // doesn't handle all edge cases (e.g. case-sensitivity on Linux, or traversing between
-            // UNC paths on Windows). SMAPI and mods will use the more robust .NET 5 version anyway
-            // though, this is only for compatibility with the mod build package.
-
-            // convert to URIs
-            Uri from = new(sourceDir.TrimEnd(PathUtilities.PossiblePathSeparators) + "/");
-            Uri to = new(targetPath.TrimEnd(PathUtilities.PossiblePathSeparators) + "/");
-            if (from.Scheme != to.Scheme)
-                throw new InvalidOperationException($"Can't get path for '{targetPath}' relative to '{sourceDir}'.");
-
-            // get relative path
-            string rawUrl = Uri.UnescapeDataString(from.MakeRelativeUri(to).ToString());
-            if (rawUrl.StartsWith("file://"))
-                rawUrl = PathUtilities.WindowsUncRoot + rawUrl.Substring("file://".Length);
-            string relative = PathUtilities.NormalizePath(rawUrl);
-
-            // normalize
-            if (relative == "")
-                relative = ".";
-            else
-            {
-                // trim trailing slash from URL
-                if (relative.EndsWith(PathUtilities.PreferredPathSeparator.ToString()))
-                    relative = relative.Substring(0, relative.Length - 1);
-
-                // fix root
-                if (relative.StartsWith("file:") && !targetPath.Contains("file:"))
-                    relative = relative.Substring("file:".Length);
-            }
-
-            return relative;
-#endif
         }
 
         /// <summary>Get whether a path is relative and doesn't try to climb out of its containing folder (e.g. doesn't contain <c>../</c>).</summary>