I was thinking the same. I considered Vivaldi for some time but it was just buggy. That's a shame because now that Chrome is going to release manifest v3, many users will look for alternatives. Vivaldi has had years to polish their UI but they have missed the train. Eventually I'll settle with Brave, I think.
I used Vivaldi for a long time and never encountered many UI bugs. About a year ago I switched to Firefox mainly because I don't want Chromium to take over the world.
What I miss most using Firefox is the ability to customize almost everything.