Nah, it's not that bad, yet.

a) Manifest v2 shutdown has been promised for years now Sure, it will come but Google has pushed it back several times already (though I'm sure it will come eventually)

b) Manifest v3 does hurt, yes. But you've got options of uBlock origin light, adguard, ghostery, and probably others to choose from for adblocking. Plus, unless the Brave browser shuts down entirely I'm sure they'll keep working on their shields and adblocking as much as possible.

c) There are browser alternatives. While Mozilla is pozzed, there are several good Firefox forks - Waterfox, Librewolf, Pale Moon, probably more. (Heck, not even sure I'd call Pale Moon a fork anymore as it has been 6-7 years since it was mostly different). And, though I am loathe for many reasons to give Apple anything, Safari is still it's own thing, not Chromium (though I've no idea of the extension availability on it).

d) People are indeed making their own browsers from scratch. Two I know of are Flow and Ladybird though again, no idea of the adblock functionality they will have.

e) PiHoles and similar exist, and while they do not stop things like in-line Youtube ads they do stop a lot of the most obnoxious ones.

f) If all else fails, we can all just go back to Lynx like it's 1993.

And probably more stuff. Will things change some, yes. But life finds a way.