Nope! Just decided to be a disappearing asshole for 36 hours and come back like nothing happened.
edit: thanks to all for the different perspectives. he is fixed, has all of his shots, and has his own temperature contolled kitty condo (aka the laundry room) that we put him into every night. we have a pretty good network of neighbors and pieced together his activities via security cameras. he's a mouser for sure and that is his job until he decides to retire.
Do you have any resources on the how for transitioning?
Ours is indoor/outdoor. We do a lot to mitigate the risks, but I'd love to have an option to slowly bring him in.
For my cats we were lucky enough to live somewhere that had very little traffic at the time, so we'd let the cats out only when we were out.
Then slowly let them out, but only in the garden area, and then only with a leash. Eventually we stopped letting them out. We'd distract them before opening doors.
I don't have personal experience of taking an outdoor cat indoors. It might be worth talking to a cat behaviourist if there's something in particular that's causing trouble.
But based on what I know, I'd imagine outdoor cats have the option to hunt whenever they feel like it, and have the option to be alone whenever they feel like it, and taking those two things away might be the main source of discomfort for an ex-outdoor cat.
It's important that a cat have its needs met, and so in your home there should be secluded/hidden/out of reach places for a cat to go and be in. You likely already have this covered, but the point is to give the cat the option to retreat and disappear from constant company.
Play, which has to replace hunting, is a little different. I keep some hard plastic too large to eat toys out at all times, but these only entertain when my boy is extremely wound up. Most of the time for it to be engaging, he needs to be playing "against" me pretending to be prey with a wand toy or laser pointer. Bouncing balls with their unpredictable movement also work really well, but he will chew and swallow those so the play has to be supervised.
I also keep sticks of matatabi (a plant with the same compounds in it as catnip) for him to chew. They're not toys, but another thing for him to do.
I also never cover the windows completely, just so he can see outside. He likes people-watching. Yet more for him to do.
When he wants to play, he will let me know, there's a certain meow, or he'll stare at me while sitting next to drawer with the toys.
So maybe try playing with your cat instead of letting it outside? Basically addressing the probable cause for it wanting to head out in the first place, which is boredom. Maintain as many things for it to use to kill time as you can, and help with it personally whenever you can be asked.
Also it doesn't take that much. Even outdoors, cats will doze most of time, they sleep several hours more each day than us.
If it seems like your cat doesn't like playing with you, look up videos of people playing with their cat. Every cat has a predators instinct, but the way to entice with play can be extremely varied. Mine goes crazy for the fluffy ball of a wand toy sloowly being pulled behind and corner and going out of sight, (like a mouse or something trying to sneak away) but won't give shit if I just wave it around in front of him.
In my experience, the best ways to modify behaviour have been changing something he wants to do so that it's unpleasant to do (sticky tape on furniture he likes to scratch, setting a metal measuring cup atop the toilet paper so it comes down clattering to the floor if he unrolls it), or distracting with play (making the cat stop what it's doing by starting a play session). A cat doesn't understand punishment, but if you change something so that an obvious consequence that a cat won't like occurs when they do something you want them to stop, they will quickly learn.