This error appeared now.
my HSTS is activated, I tried to install again using dietpi-letsencrypt and even so the warning does not disappear
the other warnings disappeared with the reinstallation of nextcloud
HTTP header "Strict-Transport-Security" is not set to at least "15552000" seconds. For added security, it is recommended to enable HSTS as described in security tips ↗.
1: Attempt to reinstall this existing certificate
2: Renew & replace the certificate (may be subject to CA rate limits)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Select the appropriate number [1-2] then [enter] (press 'c' to cancel): 1
Keeping the existing certificate
Deploying Certificate to VirtualHost /etc/nginx/sites-enabled/default
Enhancement Strict-Transport-Security was already set.
Traffic on port 80 already redirecting to ssl in /etc/nginx/sites-enabled/default