I use Phocid, maybe a bit too minimalistic regarding you used Musicolet. It is only available on F-Droid though.

• The metadata indexing (when the advanced metadata is activated) works wonders.
• UI is straight forward and simple and until now I did not encounter any bugs (LineageOS and e/OS).
• The folder structure is maintained and can be found under the “Folders” tab.
• Sound quality is good, way better than VLC (what I used before).
• Battery usage is, as far as I can tell, low

I bought a Fairphone 3 and put LineageOS on it a few years back and can recommend it. LineageOS is less secure than GrapheneOS as far as I can tell but the privacy aspect is there, as you have a completely degoogled phone. I have some friends that have the same setup on the newer Fairphones and they are also very happy and have a smoother experience than me, because it is a newer phone.

Fairphone is an European country that has a move to open source (https://www.fairphone.com/en/open-source/).

To the compatibility and functionality:

• SMS and Calling is no problem, VoLTE works and as SMS app I recommend QUICK.
• AppStore I recommend F-Droid and Aurora Store. With Aurora Store you can download and install all apps that are on the Google Store. Just check, that your Banking Apps and so on support non-Google-Android OSs as some people I know had to switch back because some banks and services only work with Google Services (and that is a shame in my opinion, a Bank should NEVER be dependent on other companies for transactions and authentication. I for my part switched bank because of such a thing.)
• microG can be used to use apps that need Google services, I do not use it but friends use it and are happy

In general you will find an replacement for every app you now use that is from a big company. Open Source came a long way and most alternatives are even better in my opinion.