Can uni see my past UCAS application materials even if I didn't apply to this uni

Do unis have access to all my past UCAS applications? Or only the unis I applied to keep my past application?

Do unis have access to all my past UCAS applications? Or only the unis I applied to keep my past application?

Not super clear what you're asing, but from your thread title:
"Can uni see my past UCAS application materials even if I didn't apply to this uni"
Only unis you've applied to this cycle can see your current application.

Did you end up in clearing in previous cycles?

I applied in this cycle (I will reapply) and I don't think I will end up in clearing

When you reapply universities will be able to tell that you have a previous application.
If you didn’t apply to them and don’t end up in clearing then they will only be able to see that not any details from your application.
Is there something that you are particularly worried about them seeing from your current application?

I study a curriculum that allows students to cancel scores. I got a poor grade on History and that might have impacted my application. I want to cancel the score so I don't have to include it in my application next year. But if they can track my old application it will be bad.

which curriculum is this?
One lower grade is unlikely to have any impact on your chances of an offer unless it's in a critical subject for the degree you're applying for

AP -advanced placement course. I applied to Philosophy and I got a 3/5 on World History(which is bad).