We're seeing a bunch of test failures on arm64 iOS/tvOS with stack traces like this one:
System.PlatformNotSupportedException : Operation is not supported on this platform.
Stack trace
at System.Buffers.IndexOfAnyAsciiSearcher.IndexOfAnyVectorized[Negate,Default](Int16& searchSpace, Int32 searchSpaceLength, Vector128`1 bitmap)
at System.Globalization.CompareInfo.IndexOfOrdinalHelper(ReadOnlySpan`1 source, ReadOnlySpan`1 target, CompareOptions options, Int32* matchLengthPtr, Boolean fromBeginning)
at System.Globalization.CompareInfo.IcuIndexOfCore(ReadOnlySpan`1 source, ReadOnlySpan`1 target, CompareOptions options, Int32* matchLengthPtr, Boolean fromBeginning)
at System.Globalization.CompareInfo.IndexOf(ReadOnlySpan`1 source, ReadOnlySpan`1 value, CompareOptions options)
at System.Globalization.CompareInfo.IndexOf(String source, String value, Int32 startIndex, Int32 count, CompareOptions options)
at System.String.IndexOf(String value, Int32 startIndex, Int32 count, StringComparison comparisonType)
at System.String.IndexOf(String value, StringComparison comparisonType)
at System.Tests.EnumTests.Parse_NonExistentValue_IncludedInErrorMessage(String value)
{
"ErrorMessage": "at System.Buffers.IndexOfAnyAsciiSearcher.IndexOfAnyVectorized",
"BuildRetry": false,
"ErrorPattern": "",
"ExcludeConsoleLog": false
} 
We're seeing a bunch of test failures on arm64 iOS/tvOS with stack traces like this one:
/cc @SamMonoRT @fanyang-mono @radekdoulik
I think it got introduced by #85303
Build Information
Build: #85303
Leg Name: Build ios-arm64 Release AllSubsets_Mono
Error Message
{ "ErrorMessage": "at System.Buffers.IndexOfAnyAsciiSearcher.IndexOfAnyVectorized", "BuildRetry": false, "ErrorPattern": "", "ExcludeConsoleLog": false }Report
Summary