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Let‘s Encrypt describing their ACME profiles in detail:

‚classic‘: 90 days, all as before
‚tlsserver‘: 90 days, smaller certs, cut lean for its server role and modern clients
‚shortlived‘: ~6 days, otherwise like ‚tlsserver‘

If you have no idea what the mentioned TLS extensions are about, do *not* configure a profile. But if you do, use classic.

If you have a rough idea and serve modern clients, tlsserver cuts some bytes and the auth process is tighter.

https://letsencrypt.org/docs/profiles/