I don’t think you can install microG in this case unfortunately, since 1: the lack of signature spoofing by your stock OS, and 2: the signatures/package name microG uses have already been used by the official Google Play Services in this case, so I don’t believe Android will let you re-use them for microG.
I would just recommend uninstalling any Google apps and Samsung bloatware and any other garbage that you can through ADB in this case if you haven’t yet. It can be a bit hacky and isn’t perfect, but its definitely the best option you have since you’re unable to install any custom OS.
I tried Gmaps WV but it still needs google play services to work.
GMaps WV definitely doesn’t need Google Play Services to work FYI, though nowadays its developer recommends just using Google Maps with uBlock Origin in incognito in a browser like Mull instead anyways.