Very little if anything at all. Depends a bit how you draw the line between an app and the base OS. Contactless payments dont work with Google Pay - but that is due to Google using attestatiom to check if the OS is GMS lincesed (GrapheneOS is not). There are alternative contactless payment options that work fine.

Moving the goalposts to "it's not their fault that it doesn't work" doesn't really change it doesn't work.