YouTube
One of the Pipe ones or Grayjay. Right now I'm using PipePipe since it supports viewing Shorts on creator profiles whereas Grayjay doesn't support that yet. Grayjay is still in early development though so it will probably be where I end up. I like their anti-censorship goals such as enabling multiple plugins and polycentric comments. Though, I usually just use the browser for most random searches anyway and just use the apps to manage subscriptions. Grayjay also supports FCast, a new open-source protocol as a Chromecast alternative.
Keyboard
FUTO Keyboard. It has built-in swipe typing and it has open-source language model predictive text suggestions and auto-correct, which I don't think any other alternative keyboard has. It's like 90% as good as gboard. FUTO Keyboard also has a built-in speech-to-text that competes with Google's in terms of quality. You can also install the FUTO Voice Input App separately if you want to use it with another keyboard like Heliboard instead.
Browser
Brave + Vanadium as a main browser. If you need a browser that supports extensions, try Mull Browser (it's a hardened Firefox browser). You can login to a Firefox/Mozilla account using Mull. Just know that Firefox-based browsers on Android don't have the best security and lack site isolation, so I only use it as a secondary browser. Cromite (fork of Bromite) is also a project worth keeping an eye on for the future.
Gallery
If you're comfortable self-hosting, look into Immich. It looks and functions very similarly to Google Photos, but it's self-hosted and privacy respecting.
Social Media
I'm biased since i don't actively use social media. But i just do it in the browser if I need it on mobile. Unless your job requires it, you'll probably benefit mentally from not having social media on your phone anyway. I mostly just browse reddit, X (Twitter), and YouTube these days, but there are privacy web-based front ends like Redlib, Nitter, and Invidious. (Some nitter instances still work for light casual browsing).
Note taking
Standard Notes, Joplin
Music streaming
Also look at RiMusic (uses YouTube Music)
Password manager
Also can look into Proton Pass, it's part of the Proton Suite.
RSS
Feeder
Weather
Breezy weather or Weawow if you want more weather sources like Dark Sky (Apple Weather)