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.
IINA is based on MPV, so I would assume that with a custom OSC, mpv can also look like this.
edit: went looking https://github.com/maoiscat/mpv-dark-box is definitely not what youre looking for, but an example. It might be possible to modify this to have a blurred background instead of a black background.
https://github.com/stax76/awesome-mpv has a bunch of info about customizing mpv, with a On Screen Controller section.