This might be useless info, but before clicking go on a selected web installer, try the show install options button.
Also, you can get a narrow phpMyAdmin instance to be the manager for all databases without having Virtualmin set it as the go to instance. Inside the Webmin → Servers → MariaDB Database Server module look at the user management, and also the one next to it, maybe database connections section?
If you tweak the permissions in those two areas, you can give one login access to all the internal databases. You can also add login credentials with any limitations you desire for a user to get at a table without being a Virtualmin user at all.
If you do this second method, really think about how your security footprint is expanding.
Reading through the tooltip on the screenshot you supplied it looks like it needs to be enabled, perhaps there is a setting in the script installer module settings as suggested by @WNYmathGuy. Personally I don’t use the script installer to install phpmyadmin as it is in the repository which means I get the version that the version of my os recommends rather than a version that may need a different version of php which I might not have installed
@Ilia I know you are busy so if this is a bit more involved that a quick answer, it can wait, but my Global Install option is missing for phpMyAdmin.
I am running Virtualmin 8.1.0 Pro, was there something I needed to do to activate the global install option so it would appear, or is this a bug that is still present, maybe a patch is available, the only patches I found were for fixing a http_auth issue.