Do you have an old Mac running Capitain… Mac OS older than 12.2, then you might get problems with a lot of web sites… even though they are safe.
This web site helped me: https://docs.certifytheweb.com/docs/kb/kb-202109-letsencrypt/
- Download the certificate from here: http://x1.i.lencr.org/
- Open the Keychain Access app and drag that file into the System folder of that app.
- Find the ISRG Root X1 certificate in System and double click on it, open the Trust menu and change “Use System Defaults” to “Always Trust”, then close that and enter your password to confirm the change (if prompted)