I had an interesting experience with a website where I registered my car to pay for parking. As I was submitting my information, I was unable to proceed as if the page had broken. This was attempted both on the android brave browser and vanadium. When I tried accessing from a profile with play services installed, I could proceed as normal. In addition there was a widget for Google pay that showed up.
This suggests that even websites may depend on Google play services to be installed. I thought you all should know this in case you have encountered any websites that happen to break on GrapheneOS, but it seems to be an edge case.