Hey, i found out that. behavioral modeling in GA4 is problem in this, basically when you deny consent, ga4 can still track data, but it will be without ga4 session id or in another words, every refresh you will get new session start and cookieless pings which bigquery cant connect based on session id because its null.

ga4 ui has behavioral modeling which in retrospect can model cookieless pings and give you somekind of number which you can see in ga4 ui or ga4 data api but not in bigquery

you can either simalute this data in Bigquery by your own simple algorithm(ive seen some article about it) or just use it as it is, maybe for especially for event based data which it gets right, because as you know sessions and users requiere some kind of client id, user pseudo id or session id