I may be the odd duck here with all the librewolf suggestions, but I am fond of waterfox, just configure it / harden it along similar lines as librewolf, force DoH, force HTTPS, have some kind of anti fingerprinting/profiling solution, yada yada.
Uh then what I do is just run I2P and use a silly little 'assign a proxy to a tab type' addon, and now that is my 'private mode' that runs in its own window.
(i ended up with this because i wanted to be able to run and manage i2pd, specifically, also as a distinct thing, and i could not figure out how to do this with any of the existing i2pd -fox land addons... maybe i am just stupid, i dunno lol)
Ultimately, what I would suggest is to just test various configurations of various security oriented browsers in the eff cover your tracks thingie, and find a balance or use style that works for you, balancing functionality and security/privacy.
Like, do actually test things, don't just run with what someone says should work, not even me.
For me, what works is my weird little --just use one browser and have a 'mostly secure' default mode, and a 'more secure' private mode--...
... but maybe you'd get better mileage out of just two totally different browsers, one 'secure-ish' and one 'more secure'... or maybe theres some other way of switching between other levels of JS blocking / ad blocking / general security thresholds via other kinds of mode shifts or something?