Thank you a lot for the extensive und thorough answer which is not just "abolish Google, raid their headquarters and delete your data yourself". It actually helps me. I know I could use GrapheneOS and remove everything Google from my life, but then again, there are certain apps I really need, which don't work without Google even if you try really hard. For example my transport tickets would be 20% more expensive if I didn't use the local transport authority's app, Signal is only distributed through the Play Store etc. etc. – what's even worse is, that these apps wouldn't even need the Play Services if the developers really wanted it.

just use a more privacy friendly SMS app and phone app.

I use LineageOS, so I guess the integrated SMS and phone apps don't do this?

better quick win would be using private and secure messenging, calling, and video chatting services

Also a good recommendation, thanks.

Most of my communication is through Matrix, Signal and Mail and I'm using encrypted phone calls through Signal and Matrix, so at least I'm somewhat safe from Google in that regard. Of course I still hemorrhage metadata, but privacy is not an all-or-nothing situation like many privacy evangelists shout into the void.