My kid is Y4.
I'll talk to anyone, or not, and have no problems either way. The parents are friendly enough, and if one ignored me I'd dismiss it as their not having seen me, preoccupied with something else, etc. It's highly unlikely to be about me personally and even if it is, I can't pretend to care overmuch.
Doubtless some cliques do exist: if they do, I'm not aware of them. If other parents are friends and meet up outside of school drop-off and pick-up, I haven't noticed and am busy as most of us are, so it would be an overinvestment to make time for transitory, school-gate friendships in addition.
That's not to say parents bullying other parents doesn't happen, just because it happens to be outside my experience. But there's a limit to what they can do. Drop-off is easy, you drop and go. Pick-up, if you do that too, is 5-10 mins wait per day.
It should take up precisely that much of your time and attention.
Sorry this is making you feel rotten OP. I know on these threads a dismissive attitude is inevitable, and I've no desire to add to that, but hope this is something you can deal with in proportion. Call a lovely friend who does have time for you and invite them for coffee, and (as far as possible) only make room for what is positive in your life. Works for me 🌹