For music production check out Ubuntu Studio. Any distro can run music production stuff but Ubuntu Studio has all the required bits ready to go.

For DAW I transitioned into Reaper which runs natively on Linux. VST support with wine and yabridge works generally fine. For Native Instruments you need to use a legacy installer. I bet there are still problems with some vendor authorizations. You should just test it out to see if your favorite VSTs are supported.

Also if i want to make a plex server on an old PC, what would people recommend?

Any desktop PC built in the last 10 years (edit: that was at least mid-range when it was built) should be fine. Just stick some hard drives in it :)

Intel processors are a good choice because their onboard GPU is quite good for video encoding/decoding. 6th gen or newer Intel Core processors (2015 or newer) would work well. They improved the H265 encoding/decoding a lot in 8th gen (2018) so that'd be even better. You can use something older but you'd need to also use a graphics card for video encoding/decoding, and it'd use more power.

Having said that, keep in mind that performance per watt almost always improves over time, meaning newer processors are more powerful even if they use the same power as the previous generation. A newer i3 will perform better than a very old i7. Using an very old, power-hungry system may end up more expensive in the long run compared to a newer mini PC.

I like using Proxmox. It lets you run multiple virtual machines on the system. VMs are good because you can easily snapshot them and revert back to an old snapshot in case of issues, and you can easily move the VM to a different system in the future. I use Unraid at home and really like it. It's a bit simpler than Proxmox, but it costs money to use (Proxmox is free for personal use).

I used to use FL Studio, but hated using Windows. I got almost all features (including VSTs) to work in Ubuntu under Wine, but had a problem with WineASIO, which I seemed to require to use the USB sound card properly.

Because of that, I since changed to a DAW called REAPER which is built natively for Linux and works flawlessly and is very nice. There is a program called Yabridge to help run Windows VSTs. I even got more complicated plugins with authentication like Addictive Drums 2 to work using Wine no problem.

If you want a fully FOSS solution there is Ardour which is also great but a little less slick than Reaper IMO.

I’d recommend checking out Linux Mint with the “cinnamon” desktop.

Installing hardware drivers and software is a breeze. It comes with a software manager for easily adding new programs.

Screenshot included for convenience:

I'd go for Jellyfin over Plex myself.

Also if i want to make a plex server on an old PC, what would people recommend?

My plex server is headless, running Almalinux. Doesn't take much, I have it running on a very old NUC8 (NUC8i5BEK). The box is also running Asset UPnP and AudioBookshelf server too.

Personally, unless the server will also be the client (as in, you'll be watching from the server box and not a streaming box, tablet, TV app, etc), I'd skip any GUI and just install it from the terminal, save your resources for what matters. Desktop environment is pointless for a server machine.

If you were buying a cheap machine to handle it today, I'd probably recommend a Beelink (or other) mini-PC with a Ryzen 5000 series chipset (5500u/5560u models with 16GB RAM can be found very cheap, generally $215-$240 new these days). The 5000 series in particular are very power efficient for something you likely will leave on all the time, and have both 6c/12t and 8c/16t variants, though the 8 core ones will probably be more like $300-$320.

Whatever you buy, if it comes pre-installed with Windows, delete the OS. I wouldn't trust preinstalled on these boxes, and in any case Microsoft is getting really sketchy with this whole Windows Recall thing anyway.