Affected Versions: 2021.2.0b1, 2021.2.0b9

It appears that it only affects some Russian Windows7 SP1 versions and other versions with non-US character sets (Japanese and Polish confirmed by users).

Callstack:
ntdll.dll!KiUserCallbackDispatch()
user32.dll!NtUserGetProcessWindowStation()
msvcr120.dll!__crtMessageBoxW()
msvcr120.dll!_NMSG_WRITE()
msvcr120.dll!malloc()
msvcr120.dll!_malloc_crt()
tbbmalloc.dll!000007fee9c90add()
msvcr120.dll!_initterm_e()
tbbmalloc.dll!000007fee9c90d00()
tbbmalloc.dll!000007fee9c90e36()
ntdll.dll!LdrpRunInitializeRoutines()
ntdll.dll!LdrpLoadDll()
ntdll.dll!LdrLoadDll()
KERNELBASE.dll!LoadLibraryExW()
KERNELBASE.dll!LoadLibraryExA()
kernel32.dll!LoadLibraryA()
tbb12.dll!000007feeaa25215()
tbb12.dll!000007feeaa25125()
tbb12.dll!000007feeaa17866()
tbb12.dll!000007feeaa173c8()
ntdll.dll!RtlRunOnceExecuteOnce()
kernel32.dll!InitOnceExecuteOnce()
msvcp140.dll!000007fef717522b()
tbb12.dll!000007feeaa177d0()
tbb12.dll!000007feeaa172de()
tbb12.dll!000007feeaa1767c()
tbb12.dll!000007feeaa2990c()
tbb12.dll!000007feeaa15120()
ucrtbase.dll!_initterm()
tbb12.dll!000007feeaa455aa()
tbb12.dll!000007feeaa45784()
ntdll.dll!LdrpRunInitializeRoutines()
ntdll.dll!LdrpInitializeProcess()
ntdll.dll!LdrInitializeThunk()

In the callstack, you can see it tries display a message box, here's the text:

Runtime Error!

Program: E:\Program Files\Unity 2021.2.0b9\Editor\Unity.exe

R6030
- CRT not initialized

I suspect this happens because LoadLibrary is called from the global constructor, but it's just a guess.

Forum thread: https://forum.unity.com/threads/unity-2021-2-0b1-does-not-start.1132336/