In my case, when I tried to install Monterey to ssd connected to macbook's own Thunderbolt 3 port, always installed but failed to boot with that, but when I install Monterey to ssd that connected to Belkin hub(or any usb hub?) then it succeed in boot and operate... I think, installation detect thunderbolt port and what is connected to thunderbolt port... if ssd that connected to thunderbolt 3 port is not thunderbolt standard device? then it is failed.... but when using usb hub and ssd to it (that's not thunderbolt speed) then Monterey thinks it's OK... I tried several times and I think this principle should work...