If you want to have a working phone, you need google apps (Google Maps, Google Play Services (used for many apps' notifications, location, analytics, etc.), Google Play Store, YouTube app). The Open Gapps project packages these nicely for use with LineageOS, but installation is janky (download a .zip file, install it using TWRP). note: despite being called "open", Open Gapps are proprietary, but packaged using open source software. Using LineageOS in this way is the sane/easy default that most LineageOS users probably choose. Using this method, you must sign in to google play services to install or update apps through the play store. Google play services includes a google analytics api, a a device registration program that generates an advertising id (so does iOS), Google also collects location data associating Wi-Fi hotspot with GPS coordinates (so does iOS). I'm not sure of the full extent of what info google collects, but it is probably substantial, and most probably happens through google play services. You could dodge this tracking by not logging in to Google Play Services and using a play store replacement like Aurora Store or Yalp (play backwards).

Another option is to use microG, a derivative of LineageOS that re implements parts of google play services with open source and throws out the rest. YMMV, but I have used it and my phone worked, excepting some apps' notifications because they use google cloud messaging. I never signed in anywhere with a google account, but I did have google maps installed (I haven't found a good replacement on Android). Google probably got rather little info from me, but they did get my location sometimes.

Or you could just install F-Droid.

I agree that most people probably need Google Play because the apps they use aren't available anywhere else.

But then again most people probably don't have the skills to install LineageOS to begin with.

Very easy; the default is to have zero google proprietary stuff. In fact, you have to jump through some hoops to get Google play store, Maps etc installed, and it's getting harder and harder as Google locks its services down.

Simply set up your default search engine to DDG or whatever you want and your LineageOS phone will send exactly nil to Google.

My understanding is that completely de-googling the phone is somewhat hard because of Google Play Services being a prerequisite for many services. I understand that you can get by without it, but many people find that somewhat of a burden.

There is also microG, free reimplemetation of Play Services: https://lineage.microg.org/

Usual warning here: microG does talk to Google servers still so it's not really Google free. Way less than Google's version though.

The main missing part is a good maps/Waze equivalent. I don't need anything else that's not available on F-Droid. Now I'm a GNU/Linux user of strict observance (depends only on Free Software!), so I probably don't have the same requirements as most.

Have you tried OsmAnd? (and if you have, what are your thoughts?)

I didn't try it, but what I'll miss the most is traffic information (I live in a very crowded area with huge traffic jams).

WhatsApp works, but you have to check from time to time since Google made Playservices mandatory for push messages. Signal and Telegram don't.