I went to this site by Mozilla:
The Mozilla Observatory is a project designed to help developers, system administrators, and security professionals configure their sites safely and securely.
Put in my domain name and scanned it.
Got this as a response:
View attachment 279047
I think Mozilla doesn't recognize "Let's Encrypt" as a trusted source. If so, that's odd. It's a reliable NPO-based certificate issuer that loads of websites use.
I could be wrong but that is what I suspect...