gnome-shell-extension-mpris-indicator-button VS KvLibadwaita

Mpris Indicator Button is pretty cool too, but seems to lack a hot key to display it.

I also use the mpris indicator extension myself and that particular dev uses Fedora (or sometimes Ubuntu), and they've said in the past they can't update the extension until Gnome 43 hits, so since Fedora is still delayed to mid-November, that extension won't be officially updated just yet. But if you check their GitHub they have a "crude" master update for Gnome 43 you can use if you really want to, but just know it's not release ready yet.

Extensions: Blur my Shell, Tray icons Reloaded, Clipboard indicator, GSconnect, MPRIS Indicator Button, Night Theme Switcher, Color Picker

There are at least two extensions which do that (for Gnome 40): MPRIS Indicator Button and Media Controls.

Since Waterfox is based on Firefox and the MPRIS implementation of the latter seems optimal I suppose something is "missing"(?) in Waterfox sourcecode, I use the "MPRIS Indicator Button" GNOME shell extension and it's always worked flawlessly with Firefox but it never did with Waterfox .

What is the difference between this and KvLibadwaita? (https://github.com/GabePoel/KvLibadwaita)

That's because i use this KvLibadwaita and adw-gtk3 themes to have everything looking the same on Gnome :>

You can also just make KDE look like GNOME with very little effort.

QT themes? This exists btw. I even have them change with light and dark theme with the extension (though i have to tell the extension to run a script to copy paste both kvantum and qt5ct.conf file to their respective folder with respective light and dark theme). Its complete baby.

There's a libadwaita kvantum theme

It's written in QT, so you need a QT theme. There's the KvLibadwaita style for the Kvantum theme engine.

Sounds like KvLibadwaita might be what you're looking for.

GTK Theme: adw-gtk3, KvLibadwaita

For QT you can use kvantum and this theme.