Snshdhsbsbsb
If you don't have a reason to specifically use the youtube app, like compatibility with other apps (Waze, Sonos, YouNameIt), you might want to switch to a different client (FreePipe, Tubular, and others).
Some clients will still connect directly to the services (so your network footprint would be the same, more or less), but you still avoid giving the app all the device data and the like.
Also, less telemetry and/or enhanced privacy overall, plus (usually) no ads.
Some other clients might even introduce a proxy between you and the service.
The same goes for youtube music, there are plenty of clients that would fetch music from youtube or spotify that would improve your privacy. Again, if you don't have some compatibility reasons, you might want to switch app.
For Fitbit, you might want to try GadgetBridge.
Nice app, I tried it in the past for other smartwatches (not fitbit), but I kind of remember it should be compatible.
As for Google Maps, I would say that navigation is trickier with other apps (because of the underlaying map), but popular alternatives are CoMaps (which I use often), Magic Earth and others.
Snshdhsbsbsb Is it even possible to make Google only access youtube and Fitbit on my phone?
Using GOS, Google has very small access to your data.
Mostly they can grab data from their apps only, with access to just what you granted with permissions.
Someone would argue that with IPC they might share data between data, but even if they really do that, it will be just among their apps, and not third party apps.
This means that if your fitbit app is not made by google, they should have access to no data at all, unless the app packs a tracker or is willingly reporting data to Google.