maybe my experience of the last days and weeks can help somone:
I am running Lineage 17.1 (February release) on my M3.
I did not increase the system partition. So eventually I could only install Open GApps pico (which is fine for me, since all other google apps can be installed as user apps from play store).
For all other Open GApps variants with more apps the system partition needs to be increased to 5GB. (instuctions see first post from @surdu_petru
In the end I didn't use GApps. I installed microG Revived on the M3 to get Google Services. Unfortunately to run apps with in-app-purchases it was necessary to install a modified play store apk. Additionally for signature spoofing Magisk's Zygic, LSPosed and LSPosed module FakeGApps were required. After some hick-ups with the play store registration and and login in my google account I got it running.
In-app-purchases worked, but I could not install purchased apps from play store (e.g. Titanium Pro, Nova Prime, AFWall+ Unlocker). Aurora store solved the issue.
That solution contained to many workarounds and I realized that my device was slow, laggy. After a restart everything was fine, but after a while again the same issues.
Furthermore the update of the play store was not possible. The modded version is 20.x.xx, which must be already a couple of years old.
So I started to look for a better solution.
I found this XDA article:
Looking to install a custom ROM? Need the right GApps package for it? Here's how you can download and install the latest Google apps.
I began to test GApps Magisk modules.
- MagiskGapps: Does not work, since it supports Android 11 - 13. LOS 17.1 is Android 10.
- LiteGApps: Could be installed but didn't work. Google Play Services crashed permanently.
- BiTGApps: Works!
So finally I found for me a clean solution. BiTGApps Standard with the minimal required component to have google services. Play Store was updated to the newest version. I got rid of microG, LSPosed and many modules. System partition need not to be modified, even if you select a more comprehensive GApps package.
Signature spoofing is not necessary. Play Store shows "certified". I am happy so far...
BTW: For SafetyNet pass still Magisk and the two known modules are required.