The only relevant question is if they track you in any different way than Facebook tracks you in incognito mode, that is, if the browser gives Google more infor

The only relevant question is if they track you in any different way than Facebook tracks you in incognito mode, that is, if the browser gives Google more information than Facebook could get. Like some non-fingerprinted but browser- and/or system-specific ID or some kind of pings with metadata unrelated to normal tracking/ads about which pages you visit and possibly which data you submit to pages. If not, then all is ok. Else they are higly misleading and possibly invading your privacy in an illegal way.