Every time I boot a new pi I always attach a keyboard mouse combo to it. It allows me to navigate easier. When I have a problem with BT controller too. I sometimes run into an issue setting a controller up where wrong button was pushed and won't change back or something. I'll use my keyboard and mouse combo to navigate to controller settings and map it again.

On keyboard
A, S keys work as A, B buttons
Arrow keys are direction pad.
Enter is start
Space is select
Page up, Page down are R, L

On mouse in menus
Left click is select option
Right click is back

@Alexander-Tolstykh
You can always combine buttons if you put a relay with double switch behind your unique button. I use it to connect my coin entry on both select from both player.