Couldn't run Windows 7, and Windows 10 ran like shit. My old PC basically got a second life with Linux.
This is Half-Life GOTY running on Wine, runs really smooth.
The only downside is lack of directX support, OpenGL is there but the integrated graphics card only supports till OpenGL 2.1, which is not enough for many things, and also slower than directX. Still, my PC feels much faster now, and doesn't scream like a demon whenever I open up a browser :)
(Maybe I should dual boot Win7(While never connecting it to the web), just to play some more games with DirectX?)
Also, my local hospital has started using Ubuntu, their old PCs also couldn't handle the heavy burden of running Windows I guess 🤣
Here's an anecdote. Recently, I got a 14yo (I believe) MSI MS-AC73 AIO (i3-2120, 4GB DDR3, 120GB SSD), mostly to use as a 1080p display, but it had a free PC inside as a bonus. For shits and giggles I started installing different OSes on it. First was XP. finding drivers was a pain but doable, since the machine is old af. But no matter what I did, Intel GPU control panel didn't want to center 3:4 games properly.
Since it wasn't working so well, I decided to go the opposite side of the spectrum and install W11, to see how horrible it would be. After many hours of convincing W11 to install on this machine (which is surprisingly not Copilot+ compliant), I finally got it to boot with a local account, with all devices recognized (including the touch screen). MFW when it runs pretty decently all things considered. I went ahead and removed all the extra crap using CTT Debloater. Played a couple retro PC games, installed FF and watched some YT, which manages to run at 1080p without dropped frames.
Now, of course, I decided to dualboot Linux, cause duh. Picked the latest Manjaro (KDE), hoping it will handle games better in case I try anything (might be an uneducated choice). Install is much easier, of course, but everything also works out of the box. My disappointment when same FF massively drops frames on YT. Touch controls technically work, but it doesn't show the touch locations and other minor issues.
In the end, I mostly use the neutered W11 (too lazy to downgrade to W10), cause it plays videos much better and W95-98 games. But if somebody can tell me how to fix Linux video playback issues, that would be great, as I want to make it my Linux daily driver.
If it's just YouTube that's an issue, have you searched for vaapi in about:config? That ancient CPU probably can't handle the video with software decoding.
I don't remember if I tried Plex/Jellyfin, but I'll check vaapi thingy when I use it next time. In Firefox settings, right? It's still weird that it works fine in Windows Firefox, but not Linux Firefox.