Banking apps work fine (I’m in the UK). Though HSBC recently started to refuse to run because I have a keyboard app installed from F-droid. But that’ll be a problem on any phone, not specific to Fairphone, I think.
There are simple workarounds you can try to fix it, see for example
github.com/linuxmint/cinnamon/issues/12994#issuec…

Firefox 141 does not honor Cinnamon's dark mode on Mint 22.1 · Issue #12994 · linuxmint/cinnamon
Workaround For Mint 22.1: dconf write /org/gnome/desktop/interface/color-scheme "'prefer-dark'" source: https://bugzilla.mozilla.org/show_bug.cgi?id=1978639#c24 If you need to automatically switch ...
GitHubI don’t know exactly what part of a separate profile you are after, so this may not be a 100% substitute, but I found container tabs in Firefox to work quite well (with some extensions to imorove UX). It’s still the same profile though, so passwords and history are shared.
If it is not indeed a new concept, it seems a great deal of people either didn’t know about it, or refused to care. Rather than be annoyed at the rediscovery, perhaps a better outlook would be to rejoice that these same ideas are reaching more people through the new words than it did woth the old?
I meant try for utopia. What you refer to isn’t that.
That is cynical. Been hearing this all my life as an excuse for why we can’t have nice things. If you don’t try, you don’t get.