FWIW, I have the same problem and I am working with Big Sur (11.6.1.) on an intel-based system. So I don't think the problem has anything to do with Monterey or the M1 chipset. For me, it's hanging at about 97% complete. I'm unable to stop the install/upgrade (I did have the prior version already installed on this laptop). A reboot of the system had no effect on the problem.