Turned out to be a coyote trap and there was a plastic link on the chain that attached it to the tree or whatever, that he had chewed through then limped home on three legs. If not for that link, he'd probably have died out there since the person who set it was clearly not checking it every 24 hours as required by law.
Luckily he was big enough that the trap couldn't close tightly enough to damage his leg and he was running around fine by the next day.
So idk if this helps, but maybe try different colors and configurations and find what your cat likes. Also tightness has a lot to do with it.
Or the cat might be OK with the breakaway collar now, due to "learned helplessness".
edit -- but of course danging by something other than a neck might be preferable...
And if they are indoor make sure they have areas to run around, be sure to play with them (they are a pet! They are your responsibility!), and watch their diet (often people let them get too fat and it takes awhile for cats to lose weight).
Given the crap that barely passes for industry pet "food" it's hard to keep an indoor animal slim (it's easier for dogs though since us can openers take them out for walks regularly). Pet foods are made to look and smell appealing primary to us can opener humans, not the pets. And dry foods are even worse for cats and dogs - they are used to stuff like grain as small part of the mice and other rodents they naturally eat, not as filler material.
PSA: Get your pets high quality food that is similar in composition to what they'd eat in nature and not highly processed crap. You don't diet on frozen pizza, burgers and full sugar soda all year, so please don't feed your pets the equivalent.
And you are encouraged to take your cats on walks. My friend runs a line across his backyard and attaches the cat's harness to it. She gets to run around and the bell makes birds very aware of her presence. Telling people to keep them inside doesn't mean you don't play with them (I explicitly said the opposite). I should refine that you shouldn't let them roam outside. On a leash is fine.
People don't realize this, but you can in fact train cats. My cat does tricks.
Ultimately, how cats deal with being harnessed even after being acclimated is extremely individual personality-dependent. I've seen some happily walk like dogs. Mine don't particularly want to walk alongside people and very quickly want to go off under plants or other places where they can hide and stalk, and where people can't easily go. We take them out for as long as both they and we can stand, and don't jerk them around.
The Kitty Holster type harness is significantly less escape-prone than say the PetSafe style of nylon straps, and probably less uncomfortable as well.
A couple months ago my friend found his cat dead after her collar caught while jumping over the fence. Poor little baby beast. :/ I look at my fun-loving critter basking in the sun as I write this and it breaks my heart to imagine her suffering like my friend's poor cat did.
Example of a collar with elastic segment: https://amazon.com/dp/B07P8V374M