i installed lets encrypt along with auto renewal while i was using apache. Several months ago i moved to Nginx, and today can’t access my website because certificate expired. Which i’ve never encountered before. I assume this because the webserver migration.
The easiest way be to get new certificates issued via zerossl. Add these somewhere resonable and then configure them as per the Mozilla TLS guide. https://wiki.mozilla.org/Security/Server_Side_TLS
You can then spend some time configuring certbot to work with your NGINX server.
There are plenty of online articles on how to do that