In my testing most of the apps don't work without gapps so you can just install microg and Aurora in that case. But I use only FOSS apps now so idk if anything changed.
I have definitely installed a handful of APKs over the years that did not work for me because they required Play Services, but that is far from being most of the APKs I've tried.
Well the apps I tried to install were mostly games because there are FOSS alternatives to almost everything that doesn't require Play Services and/or Play Integrity.
Wait WhatsApp works on degoogled phones? I heard they started banning custom ROM users recently and degoogled ROMs can't be spoofed to look exactly like stock ones so isn't that dangerous?