I do want to remove my account there.

But when I was doing it, I got a big warning that anyone could come up and register that handle for themselves. So I instead ended up just deleting every post, my personal details, and left the account alone (not using it anymore).

I know they do this intentionally (it's bad intentions all over the place on social networks nowadays, except HN, of course).

I'm terrified of somebody else just creating the account with the same handle I used to have, and impersonate me across old friends and contacts.

What do you suggest?

You can just inform your friends that you will be deleting your twitter account

Pin a post that you leave X (or any major SM): say its your last post because they have become a greedy, amoral cesspool and add links where they can find you instead.