Not sure about expert, but I built many custom roms for phones. GPS is not tied to Gapps, microG or otherwise.
Some apps may require Gapps to work, but any GPS only app should work fine. I use Trekarta and opentopomaps and satstat without issue and I have no gapps or microG on my phone.
You might want to check that your GPS is on. E.g., “location” tile in your drop down menu.