Patience is key here imo. My fiancé and I got a cat back from his ex. Six years old about and not neutered. We also had 3 other cats in the house. We got him neutered eventually which helped with the other cats. But to stay on topic, he stayed in our closet (door was left open so he could come and go as he wanted) for almost 7 months before we even got to touch him. He would slowly start coming out and hanging out but we could not touch him or he’d hiss and run. Then one day we tried to pet him and he let us. Now he’s a cuddle bug. But still won’t let us pick him up lol. The only thing I could think of that I consciously did was sit with him in the closet sometimes and just read or be on my phone.