It might be something as simple as ownership of the nextcloud install. I am not familiar with softaculous, so you will have to figure out the translation, but, on ubuntu Linux for example, where you have installed nextcloud into /var/www/html/nextcloud, you have to assign ownership of directories:
sudo chown -R www-data:www-data /var/www/html/nexcloud
This gives apache rights to own and thus read/write to the files that’s needed to get nextcloud to work. Remember that you also have to give ownership to the nextcloud data too, which may be in the same directory (not a good practice btw). It’s a simple fix if this is your problem. Good luck.
Andrew