I have something very similar with my sister, although I know her well enough to understand why, even though she would never admit it.
It’s not because of anything I’ve actually “done”, it is because I have some things she dearly wants, reasonable (nothing fancy) job, husband, child, and her life hasn’t worked out that way. Over time, she started putting up barriers between us as a kind of defence against her own pain/disappointment.
I tried so hard to, gently, break those barriers down, but eventually I realised I couldn’t do it for her. We now bump into each other at family events every year or so, and she’ll be absolutely gushing about how happy she is to see me in front of everyone, but she still refuses to make plans with me, or accept any invites. It makes me so sad as we used to be so close and she used to be so close to my dc.
So I’ve stopped pushing. I mostly leave her be, send no pressure invites if inviting rest of family somewhere (she is always busy), ignore if she has a "family" thing and I get missed off her invite list, and play along with it, because sometimes you just have to accept that you can’t fix something for someone who isn’t willing to acknowledge it themselves.