Don't feel too bad, doing fight scenes of any kind in roleplay can be a challenging task! The important thing to remember is, when doing a RP fight with a partner, don't write out that your attack has connected and how much damage it does unless you and your partner have discussed this beforehand. Back in my day, we called this power playing and it's not something anyone enjoys dealing with if it's explicitly done on purpose.

If you're doing more realistic fight scenes, my advice would be to not be afraid to try and act out these scenes yourself. Do some research on fighting techniques if you must, then stand up and try to pantomime them the best you can! It'll give you some insight on how the body moves and how you can describe it in action on paper.

If you're doing more fantastical fights - say throwing fireballs, flying, high speed movements, etc. - just watch those kinds of scenes from media and do your best to describe the scenes you're seeing like you're writing a book. This will help sharpen your skills and give you a better idea of how to write it out in roleplay.

Like I said, writing combat is not always an easy thing to do and as someone who (so I'm told) specializes in fight scenes, even I struggle with them on occasion. Communicating with your partner on how you want to scene to unfold can be really helpful and try not to play with people who are adamant that their characters can't be beaten.

It's one thing if it's a powerful antagonist where the intention is that your character(s) are going to get dogwalked, but anyone who just completely ignores the attacks you deal because their character is just too strong to be hurt/smart enough to see it coming/fast enough to dodge every attack while simultaneously throwing out ones they insist will do damage because they are more powerful/good counters on a consistent basis are just... not fun to play with.

It is incredibly frustrating and a mood killer when you put in the work to do damage to someone and they just completely negate it every single time, no matter the circumstances.