Lens cap for Gopro 9 (32mm square) with small tab for grip and inset to not rub against lens even when pressed on.

Depending on Your printers tolerance, scaling down to 99% may be good for a tight fit, or a small horizontal expansion (like 0,1mm) - but again, depending on Your printers tolerance. Note the small ribs on the inside allowing for some material flex even when printed in PETG or PLA.

Otherwise an easy print, place with flat side down and no support - standard 0.4 nozzle and 0.2 layer height works well.