I would say keep two browser.
For me I have Ironfox as main. And Cromite as secondary browser. Both are open source.
Cromite fulfills some of your requirements like dark mode for web,bottom search, ad and tracker blocker and that clear browsing data on exit
I would say keep two browser. For me I have Ironfox as main. And Cromite as secondary browser. Both are open source. Cromite fulfills some of your requirements like dark mode for web,bottom search, ad and tracker blocker and that clear browsing data on exit