I said “typically” because Let’s Encrypt doesn’t control key rotation: the issuance managing client (like Certbot) does.

But AFAICT, Certbot has rotated private keys automatically on reissuance since at least 2016[1]. There’s no reason not to in a fully automated scheme. I would expect all of the other major issuing clients to do the same.

[1]: https://community.letsencrypt.org/t/do-new-private-keys-get-...