The system crashes once every 30-60 minutes. However on certain kernels the crash seems to only affect the Window Manager and certain VMs - so after being logged out you can log in again and restart them. QubesOS freeze, crash and reboots with 5.15 kernel - #18 by Alethia
You shouldn’t create and use the USB qube, it either restricts you from starting Qubes or the qube itself will simply not start (depending on kernel).
It might be necessary to continue using 4.1 for now and wait for a future version of Qubes.