You should NOT use the ubuntu Certbot package. Instead you should use the snapd distribution. Certbot stopped supporting distributions in favor of snapd several years ago; their team recommends against using distribution packages because they are often seriously out of date and miss important fixes and updates.
you can delete the /csr/ files. they are only there for archives/backups and are not used for renewal.
See: How do I clear the old data from the / etc / letsencrypt directory? - #2 by _az
Adding:
This was fixed in newer versions than what your ubuntu is running.
Ticket: Purge old private key material · Issue #4635 · certbot/certbot · GitHub
Fixed in: Deprecate {csr, keys} dirs & automatically truncate lineages by alexzorin · Pull Request #9537 · certbot/certbot · GitHub
Release: (certbot/certbot/CHANGELOG.md at main · certbot/certbot · GitHub)
2.3.0 - 2023-02-14
- Certbot will no longer save previous CSRs and certificate private keys to
/etc/letsencrypt/csrand/etc/letsencrypt/keys, respectively. These directories may be safely deleted.