When you click on ‘check configurations’ in Virtualmin, does it also detect 7.4 only or also 7.2? Is your php-fpm also listed as 7.4 or 7.2 in your dashboard.
if you’re using cli updater for nextcloud, you have to check what php-cli package you have installed (that’s the debian name, don’t know about centos).
Wondering if additional php packages needed like php-redis and php-apcu. Would at least compare modules from old to new setup. NC config.php may also need to be edited and not point to 7.2. Might be better to post on the nextcloud forums.