If you're looking for a challenge you could try FreeBSD. While not Linux it's still unix like and can provide a great learning experience. I believe they have retroarch in their packages, and I've seen videos of people getting Steam working. They provide excellent documentation on their OS as a whole.

Do movies getting the Rifftrax treatment count? If so, then Birdemic.

Lots of great options here. Just wanted to add it may be worth using KDE if they're transitioning from Windows. I try and get the look visually close to what they previously had so they're not fighting against muscle memory.

Proton has a free package with unlimited bandwidth. It doesn't offer as many countries or advanced features but it works just fine.

I'm fortunate to live in an area with two wired broadband providers. And wouldn't you know it, they don't have to enforce data caps here for some reason. I'm sure it has nothing to do with the fact that a customer can leave whenever they want.

I think it depends on your use case. For my gaming desktop I use Fedora to get the latest packages. For professional scenarios I've been using Almalinux the past couple of years. It started life as a RHEL clone, but since RHEL changed their code distribution rules I see them more parallel in the stream rather than down. It's completely free, but there are options to purchase support and live kernel patching if required.

If you want to go the Suse route, Opensuse Leap will give you the closest experience to Suse enterprise. I believe Suse actually offers conversion tools to convert Leap to the full enterprise OS. I don't have personal experience with it, but have considered it in the past and this is the information I recall.