Just wanted to use the endpoint lately and find this post now. So… affected as well in version 7.9.3 (Developer edition) and a bit disappointed because this seems to be the only (offered) way of filtering projects for the quality profile.
IMHO that is a bug and needs @MODERNWEB_MW: Can you help to advise on how to catch a devs attention here?
next to that this thread is related to Quality Profile of Project where they found a workaround.