We've seen some examples where the 64-bit version of Raspberry Pi OS is failing on boot - not enough examples to consider it a widespread issue, but enough that we've noticed it!
We've found that editing a line in the config.txt file can resolve this. You can edit this file by inserting your MicroSD card on a PC, and then opening the config.txt file with notepad or another text editor.
Once open simply change this line:
Save the file, pop the MicroSD card back into your Raspberry Pi then try rebooting again.