Hey all, I'm considering upgrading from 2021.3.9 to 2021.3.21 in an M1 MacBook Air.
Does the issue exist in both versions?
Is it persistent or does the project launch after a couple of tries?

I've had this issue with a Windows standalone player (not on a M1 machine) when running multiple instances of my build at the same time (doing multiple environment training with ML Agents). My stack trace is a little different. This was with Unity 2021.3.10 LTS.

=================================================================
Managed Stacktrace:
=================================================================
at <unknown> <0xffffffff>
at System.Object:__icall_wrapper_ves_icall_array_new_specific <0x0006d>
at System.Array:CreateInstance <0x00032>
at Opsive.Shared.Utility.Serializer:BytesToValue <0x00152>
at Opsive.Shared.Utility.Serialization:DeserializeFields <0x000fa>
at Opsive.Shared.Utility.Serializer:BytesToValue <0x0179a>
at Opsive.Shared.Utility.Serialization:DeserializeFields <0x000fa>
at Opsive.Shared.Utility.Serialization:DeserializeFields <0x00212>

I've had a similar problem intermittently on an Intel Mac for several months when opening projects with the WebGL platform. My bug report was closed due to lack of a clear repro case. It happens rarely but when it does, it will typically happen multiple times in a row as described. I have to then load the project with iOS and then switch to WebGL in the editor.

Here's my stacktrace from 2021.3.4: (it's happened with various 2021.3.x versions and macOS 11 and 12)

#0 0x000001571f3bc2 in GC_is_marked
#1 0x000001571bf0c6 in mono_push_ephemerons
#2 0x000001571f2059 in GC_mark_some
#3 0x000001571f1797 in GC_stopped_mark
#4 0x000001571f12e8 in GC_maybe_gc
#5 0x000001571f1dc6 in GC_collect_a_little_inner
#6 0x000001571f7c12 in GC_alloc_large
#7 0x000001571f4178 in GC_generic_malloc
#8 0x000001571f7f61 in GC_malloc_kind_global
#9 0x000001571bfb58 in mono_gc_alloc_vector
#10 0x0000015716650e in mono_array_new_specific_checked
#11 0x00000157166622 in ves_icall_array_new_specific
#12 0x000001108853cf in (Unknown)
#13 0x000001557f3683 in Burst.Compiler.IL.DebugInfo.PortablePdbInstance:Initialize (Mono.Cecil.ModuleDefinition,System.Collections.Generic.List`1<string>,System.Action`2<Burst.Compiler.IL.LogMessageType, string>) [{0x7fe7453de3c8} + 0x283] (0x1557f3400 0x1557f394a) [0x14ed7c7e0 - Burst Child Domain]
#14 0x000001557f111b in Burst.Compiler.IL.DebugInfo.PortablePdbCache:AddEntry (Mono.Cecil.AssemblyDefinition,System.Action`2<Burst.Compiler.IL.LogMessageType, string>) [{0x7fe7453ddec8} + 0x14b] (0x1557f0fd0 0x1557f133a) [0x14ed7c7e0 - Burst Child Domain]
#15 0x000001557e18db in zzzUnity.Burst.CodeGen.AssemblyLoader:RegisterAssembly (Mono.Cecil.AssemblyNameReference,Mono.Cecil.AssemblyDefinition) [{0x7fe744e12d60} + 0x14b] (0x1557e1790 0x1557e1943) [0x14ed7c7e0 - Burst Child Domain]