Edit: I'm now enlightened and use mpv, I really like the ModernZ OSC (on-screen controls), and uses config files.
IINA is only on macOS. I looked up linux alternatives but none of them seem to have similar looking UIs, at least out of the box. I want the player UI to float on top of the video + with a blurred background, it as shown in the image; or at least the ability to theme it like so.
Absolutely you're likely talking about this right?
https://github.com/Zren/mpv-osc-tethys
With thumbfast installed too.
Personally I use a fork of ModernX:
https://github.com/zydezu/ModernX
MPV is crazy. Got a plugin that let's me clip videos very easily, one that let's me pick stream quality for when I use MPV to watch twitch videos, you can even get riscord rich presence if you're into that thing.
Here's the awesome page:
https://github.com/stax76/awesome-mpv?tab=readme-ov-file#on-screen-controller
Edit: and the official list linked from their site: