Sidebery has a form of Tab Groups called panels (see: https://imgur.com/Za9lwej) that are built into the functionality. I also have just found Sidebery to work a little better than any of the alternatives. But they're not too far apart.
Yup, tried sideberry, tree style tabs, and simple tab groups since I think there was a Mozilla page they suggested those three. None of them felt as usable as native tab groups in any of the other browsers that support tab groups (or workspaces, profiles, or whatever else their approximate implementation is). Especially in terms of interactions with other tab-related extensions. Part of the problem with having that be a non-native feature.
That's kind of the opposite of my experience. Can't leave Sidebery, it's so well integrated and usable when combined with a couple userchrome.css tweaks that any other browser simply feels subpar to that; not nearly the same attention to detail.
Do you have links to the userchrome tweaks that you use? I hear that mentioned a lot as a way to make sideberry better. IMO, the default for sideberry isn’t good. The few tweaks that weren’t outdated made things a bit better, but nothing really hit the mark. Like I said above, very willing to give suggestions a try.
edit: my main worry with relying on userchrome tweaks is things falling out-of-date or abandoned. I saw this a lot in my testing.
I only hide the main tab bar and sidebar header, both tweaks are copied verbatim from [0] (which is linked from the sidebery github readme) and the size of the window buttons block is corrected manually in a var.
Yes, tweaks going out of date was also my concern, but they're already a few years old and nothing broke so far. I reckon I could just adapt them if anything breaks, they're easy.
https://github.com/mbnuqw/sidebery