Let’s Encrypt will be reducing the validity period of the certificates we issue. We currently issue certificates valid for 90 days, which will be cut in half to 45 days by 2028.
This change is being made along with the rest of the industry, as required by the CA/Browser Forum Baseline Requirements, which set the technical requirements that we must follow. All publicly-trusted Certificate Authorities like Let’s Encrypt will be making similar changes. Reducing how long certificates are valid for helps improve the security of the internet, by limiting the scope of compromise, and making certificate revocation technologies more efficient.
Openssl can do everything.
That’s right, but instead of the word derived we use “issued”
Correct certs get old by design, they can also be revoked. As another commenter mentioned the biggest pain is actually in the redistribution of these end certificates. In enterprise this is all managed usually with the same software they use for deployment or have auto enrollment configured.
You should find tons of guides just take it slow to understand it all. Understanding certificates in depth is a rare and good skill to have. Most sysadmins I come across are scared to death of certificates.