The simplest way to get MicroG enabled seemed to be flashing NanoDroid (22.9.20200910) after switching the Phone to LinageOS. Unfortunately that didn't work for me (that means: signature spoofing didn't get enabled, which is apparently needed for things like push notifications).
As I didn't find any other simple solutions, I decided to try to add the signature spoofing patch myself and build the ROM with it.
These are the steps I took, that resulted in an installable, generally working build (I use Linux unless otherwise noted):
I got 2 questions:
1. By flashing NanoDroid do you mean that you tried to flash the MicroG components or did you try to use the patcher as well ?
2. Did you try to use SmaliPatcher in order to create a Magisk Module enabling signature spoofing ?