The explanation is clear, but for some reason you've removed the "It produced this output:" question from the questionnaire.
As @griffin already said, there is a missing HTTP to HTTPS redirect. Your HTTPS is working fine, but you don't notice it, unless you type https:// manually due to the missing redirect.
Certbot with --apache should have asked you if you'd like such a redirect. Maybe you've entered "Yes" there and something went wrong, but without the actual output, it's hard to say. You can reread your output in the log file in /var/log/letsencrypt/.
Also notice that you've already managed to issue four certificates yesterday! Do realise that if there is an issue with the installation of a certificate or something else not certificate issuance related that it's unnecessary to reissue the certificate time after time again. This could lead to rate limits and in my opinion is plainly abusing the free Let's Encrypt service by using precious resources for no good reason.
Please find the issue for the missing redirect without issuing any more certificates: you've got plenty, the certificate is working fine, just a missing redirect.
Nextcloud sets the Strict-Transport-Security HTTP header, so once your browser loads the site through HTTPS, the HSTS info is saved. Therefore it will look like there is a redirect in place for @leon47331, which actually is just the browser defaulting to HTTPS due to HSTS. No redirect in place indeed.
@leon47331 Please use webbased checkers such as the one used by @griffin and not your browser.