On a working phone there is a way: In settings go to Security & location > Device admin apps and disable any options that are run by “Google Play Services”, e.g. Find My Device or Screen lock service.
After that back in Apps & notifications > Google Play Services the Disableing option should no longer be greyed out.
However, on my FP3 I wasn’t able to go that way because during the 10-seconds-reboot-loop the changes made don’t seem to be saved… Too bad!