In the initial insiders build of the windows 11, some few programs simplely freeze and you can't even kill the process. The steam is a program that don't open if you already have a instance running.
As a workaround this is a small patch that are able to 'remove' the steam anti multiple instances in the same machine.
The patch is made by replacing this 0x74 value to 0xEB in the steam.exe file
I recommend you try patch by yourself finding the patterns around the 0x74 in my screenshot
Anyway, you can try my patched executable as well: https://www.mediafire.com/file/gi4lw8f2ttsen0g/MultiSteam.exe/file
If even with this you still had problem, you can add this patch as well:
this is the my patched executable with both patchs: https://www.mediafire.com/file/n50rnsnaugljjn9/MultiSteamB.exe/file
The steam can try remove your patched executable, to prevent it you can need launch the steam with -noverifyfiles or simply don't modify the original steam.exe, just left your modified one with a new name and launch the steam with him, then he don't will detect the changes