I experienced quite the same after updating my XA2.
On 3.4 most of my android apps worked really well, only the one or other small issue like missing current map position in Lime app but also the ones requiring Google Play Services were working.
After update this stopped, apps like Lime were showing: Google Play Services updating…, but not showing map or some of the apps just crashed during startup, e.g. Family Link.
Also WhatsApp suddenly had issues with media, but that thing I could solve following this thread.
I searched bug reports for Play Service or microG issues but it seems that for most of the people it was working fine after update. So I thought maybe there is a problem with my initial Play Services installation and already thought about a re-flash.
Then I took a last chance and luckily I was successful and could restore all functionality I had before just by following again the same guide I used initially just adapted to new Android version 9.
So I downloaded opengapps ARM - 9.0 - nano version and followed instructions but ofc adapted to download filename. There was one error with resource Core/gmssetup-all.tar.lz which obviously is no longer contained in 9.0, this one I just ignored. After replacing system.img and restart of aliendalvik everything worked again like before update.
Single remaining issue is that GMaps still crashes during start but that’s not crucial for me atm.
HTH,
cheers