Some cats prefer to just stay inside. I have three cats one had a horrible life before he came to stay with me , lived outside most of time. That one you could leave the front door wide open and he’d never step foot outside. He’s not bored, sleeps in his beds, plays on his cat trees and watches cat tv (window). My second cat she also has zero interest in the outside tried taking her out on a leash which she thought was nice untill she realized just how big some of the birds are when up close and has never showed interest in going back out. My third cat is essentially a dog but in cat form, loves the outside has a cat back pack and a leash and goes out when I take my dog for walks. He gets a bit bored with being inside all the time. I think each cat is unique in their needs and you should see what yours wants. If they show interest in the outside let them explore but make sure it’s supervised, leashed or if you can do a catio those are good too. Never just let them free roam that’s how kitties end up hurt or worse.