Preinstalled incompatible signatures: microG & Pdf Viewer Plus (GSnathan)

I just successfully installed the FP3+ beta on my new FP3+.

I installed F-Droid and added the official microG repository.

Sadly I can’t update microG this way, because the signature of the preinstalled microG differs.

Later on I also installed Aurora-Store (an alternative PlayStore frontend), which offered me an update for “Pdf Viewer Plus” (by GSnathan).
Sadly I also couldn’t update that app because of a differing signature.
adb logcat:
PackageManager: Package com.gsnathan.pdfviewer signatures do not match previously installed version; ignoring!

Is it normal, that /e/ delivers apps without their official signatures?
Or is this just because of the FP3+ beta state?

Workaround for microG which works fine for me (I need this for the “Exposure Notification” API which just got available with the latest microG update).

Looks like eOS explicitly delivers a custom microG version.
So it’s standard eOS behavior to have a different signature on the microG app.

Another P.S.
If you like to keep/reinstall the Magisk microG installer after an system update, you need to keep TWRP and reflash Magisk via TWRP. To achieve this you need to run TWRP A/B Retention Script (twrp-keep) (from Magisk) before rebooting when you just accepted the update installation. See also: