mine: for reddit there was fatbird i also considered spyke (i no longer use reddit) for lemmy theres wefwef/voyager and thunder for YouTube there's revanced, newpipe sponsorblock and clipious for instagram i have instander installed but im having trouble figuring out password things
Technically, I still use a 3rd party app to browse Reddit, Firefox. I use ublock origin to block ads. In new reddit on mobile, if you go to account settings FIRST and THEN enable desktop mode, you get this mobile version of reddit that's actually usable and shows post pictures full screen when scrolling through the feed.
But I've been using jerboa for Lemmy more and more lately. I used to use slide for reddit, and they are making slide for Lemmy. I wish them a speedy development cycle.