Halo,
For this issue, surely the php was not installed.
I had the same poblem, and i just install the php and restart the web service again.
Everything become OK.
Thks
Its very late, but i had this problem too…
For me the solution was enable the mod using:
a2enmod proxy_fcgi setenvif
a2enconf php7.4-fpm
After this restart apache
systemctl restart apache2
If do not work, try to purge the mod, re-install
apt purge php7.4-fpm
apt install php7.4-fpm
and if not enable automatcaly, manualy enable the mod using again:
a2enmod proxy_fcgi setenvif
a2enconf php7.4-fpm
After this restart apache and refresh the webpage
systemctl restart apache2
There were two issues, one with Apache2 and one with a fresh Nextcloud install (independently of Apache2), both fixed via live patches and for next release, of course:
So it should work with those applied. The patches will be offered via banner or by running dietpi-update.