Instead of booting while holding down ⌘⌥PR, try powering down, disconnecting from any external power source for at least 30 seconds, then reconnecting the power and starting up again. This works in cases where the ⌘⌥PR sequence does not. With Catalina and Big Sur when you are booting while using keyboard options like ⌥, ⌥R, or ⌘⌥R holding the keys down until you see the Apple logo is not enough, you must continue holding the keys down until you see a progress bar. (NOTE: I have often thought in this case, a third arm and hand would be very useful. 😉)
