[deleted] I don't think there is a "unified" approach. Your best bet is to find out if there are any google free custom roms available for the particular phone/model. Then you'd need to install MicroG on top of that if you want to have extra app compatibility/functioning.
[deleted] strip of google dependencies, yet make them "fully functioning"
The expression "Fully functioning" might be a bit of a stretch here. Depends on what you mean. The most fully functioning de googled phone i know is pixel with GraphoeneOS. All the rest have various levels of "functioning", but less.
The other alternative is to build your own custom rom by taking LineageOS or GrapheneOS and finding and adding the drivers for your particular phone to the rom. As you can imagine this is not much of an option for the average person.
Generally, ROM availability is what determines whether a phone could be degoogled or not. Unless you are a rom maker.