Been using Vivaldi [0] on and off for the last few years. Now trying to run it full-time the last couple weeks (thanks to Microsoft's questionable Edge "additions" and avoiding Chrome for any non-Google sites).
Still has a couple quirks I'm getting used to (e.g. no touchpad gestures for history navigation), but the customization is great. It is partially closed-source, but they are open about what they do [1].
The Steam Deck also gets a vote from me, but with a couple caveats. First, if you're just now reserving a Deck, availability is currently slated for after Q2 2022. It's already been delayed once, it might be delayed again, thanks to component shortages. And two, it will be using Arch Linux under-the-hood, which can both be a blessing and a curse, with regard to compatibility and usability (though I trust Valve to get most of the issues ironed out). If you're so inclined you will be able to install Windows on it.
Still has a couple quirks I'm getting used to (e.g. no touchpad gestures for history navigation), but the customization is great. It is partially closed-source, but they are open about what they do [1].
[0]: https://vivaldi.com
[1]: https://vivaldi.com/blog/vivaldi-browser-open-source/