Rolling out LetsEncrypt for a self-hosted Nextcloud instance is absolutely trivial. There are many reasons corporations might want to roll their own internal CA, but simple homelab scenarios like these couldn't be further from them.
Traefik (by default) will attempt certificate renewal 30 days before expiry. Perhaps the defaults will change if the lifetime becomes 45 days. I don't think it's possible to override this value, without adjusting the certificate expiry days, but I've never felt the need to adjust it.