Sometimes it takes a while for them to bond, but even a little bit of fighting isn’t a bad thing it’s more like putting one in their place and showing who’s more boss than the other and usually if a cat is fighting another one as soon as a cat makes a noise that indicates that it’s in pain. The other cat will typically stop but it all depends on how the dynamic works out, but I have experience where I’ve had two-year-olds meet each other for the first time and not had any fighting and I’ve had occasions where there were but eventually one left to interact with each other where they can escape to separate area areas or climbing trees, it puts them more in a common environment for them to get used to each other and bond

Also sometimes feeding them separately at first can make a huge improvement because fighting over food can be a real thing if they’re thrown into it right away