I used Avenza Maps in the past for offline navigation at various state parks. The park service provides maps and the app will let you navigate the trails. It's been a long time since I used it and I now have a new phone on which I never installed the Google Play services. The app is complaining that "check that Google play is enabled. .." and then quits.
All the sites I've searched show you how to install or enable Google play (which I don't want). I'm pretty sure that it's needed because the app allows for in app purchases, which i don't need. I don't think I rooted this phone. Are there any workarounds or shim/simulation apps that would allow the app to work without installing privacy violating Google services?
There are free and open-source map apps. Trekarta and Alpi Maps are focused on hiking/outdoor, like Avenza. Most features are probably also available on the more general-purpose Organic Maps as all of these are based around OpenStreetMap.
I personally wouldn't trust a proprietary app with my location data, much for the same reasons I don't trust Google software on my phone.
This is just an example. There are apps like dating apps, government apps, ticket apps etc that require Google Play services. In my country there were plans for train tickets to be issued exclusively per app, this is a whole other political problem, but the point stands that Google Play services become increasingly important for regular bureaucracy and societal/social participation. We should of course fight against that, but microG and others often cannot keep up.
I have and use OSMAnd and love it. I'll check out those other apps. Mostly, I want to use the trail maps provided by the park. I've been burned in the past when using other trail apps.
To my knowledge OsmAnd works fine without Google services, and is fully open source. Based on open street map, which others have suggested as well.
Alternatively, to more directly answer your question, there are apps that emulate the Google API. Look into GmsCore (GitHub), or cancer microg, maybe as a starting point. I'm not 100% on which part of the Google API they provide, and if it's the part your app relies on.
Osmand is great for most of what I need on a daily basis, but on a trip a few years ago, some of the hiking trails were not up to date and we got lost. It wasn't terrible, but it was uncomfortable and fortunately we had paper maps.
I would like to use the maps provided by the park or forestry service since I like to think that they're current, but they rely on Avenza which relies on Google. I'm okay taking a risk on Avenza for the short duration of the trip and plan to not give it network access, but I doubt I could do that with Google Play services, much less cleanly uninstall it after the trip is over.
Hilariously the Google Maps app itself works without Google Play Services, that one was a surprise to discover (and obviously pretty useless if you're trying to avoid Google's tracking)
In OpenStreetMap's, you can record tracks, so you could use a different phone temporarily to use the proprietary trail app and use a secondary device to record you hiking that and then put that on the map for the next person who goes to that area. Maybe install the trail app on your SO's device while you record the track in osmand on yours