At least I ignore the last two messages on my system. Imagick is deprecated I think and I don’t use passwordless webauth, so I don’t need gmp / bcmath. If OP also don’t use this, he can ignore them as well.
The first messages are more important, but I wonder if OP installed nextcloud via dietpi-software or not. Normally the nginx config should include this.
config files when using nginx and nextcloud is in a subfolder of the webroot