Sometimes my spools (especially cardboard) are falling down. To prevent this I made this stopper.
You need to disassemble rotary spool holder and change cap.
Second option is stopepr with wheels, I use it with cardboard spool. just put wheels into stopper and use filament and lighter to fix in place. You can make your own wheels in Bambu Studio, hole 2,5 mm, width 4 mm, just choose diameter.
I also load thread stp file, so you can make another options for your needs.