Indoor cats live longer but outdoor cats get far more mental and physical stimulation. So if you ant to keep your cat safe and healthy, you need to provide an enriching environment to keep your cat happy.
Consider getting puzzle toys to let your cat practice its hunting skills. Then provide plenty of safe spaces where your cat can eat and hide. Finally, rotate your cat’s toys to keep it stimulated with something new.
Just as people get stir crazy stuck at home all the time, so can indoor cats get bored unless you actively work to make their life exciting.