I didn’t tell you to do that, though? You can keep using MySQL. Just make sure when you switch repos, you don’t switch databases, too (I told you how to do that, I think).
You don’t need the beta version. Virtualmin 7 installer is the one you get when you download the install script now.
Always the one you are most comfortable with. I will never say anything else about distro choice, no matter how many folks ask (and it gets asked all the time). You’re maintaining a complicated system, you need to know how it works. Virtualmin papers over a lot of differences, but you’re still a system administrator.
If you aren’t comfortable with anything yet, I prefer Rocky 8 or 9, and I use it for my own production deployments. Many people prefer Ubuntu, and that’s OK, too, just use an LTS release, and spend enough time with it to be comfortable with it. No matter what OS you use, you need to get comfortable with the way the OS does things; we do things as close to natively as possible (with a few minor exceptions, which are compromises to make it possible to support so many distros with so few people…like we use firewalld across all distros, for a variety of reasons).
Fix what? There is no issue. If you installed using the Virtualmin 6 installer, you have MySQL as your database. That’s not an issue. That’s just a fact.
If you upgraded your OS to an unsupported version (e.g. Jammy), then the Virtualmin 6 repositories do not have support for your OS. That’s also not a huge issue…you’re already installed. We don’t provide very many binary packages for Ubuntu, and the ones we do provide are the same across focal and jammy. You can just keep using the Virtualmin 6 repos. Our focal packages are fine on jammy.
If you need to switch to the Virtualmin 7 repos (I’m pretty sure you do not), you have to do what I said above, because it will force a switch from MySQL to MariaDB, and it will not do it politely or safely. Now that I see where you are and what you’re doing, I think I led you astray. Just stop messing with your system. Leave the focal repo enabled. It’s fine.
Don’t go out of your way to break stuff.