GF fiber jack directly to RAX120 skipping GF network box

After unsuccessful attempt to connect ORBI RBD852 to my 2.4 Ghz devices, eventually returned, bought RAX120 thinking this would resolve my issue of connecting more wifi devices to the router as GF network box is pathetically incapable of connecting more than 12 devices (i was told by their Tech).  But had speed issues - Ookla and fast.com spped shows 120 to 200 Mbps tested on galaxy S10+ very near the router whereas GF network box gives 350 to 500)and NG support identified defective router and i replaced the same twice - now I am working on the third.  during this process, NG support stated that if both GF network box and RAX120 are in the same network, the speed of RAX120 will never improve.  Talked to GF support - one rep stated that GF network box can be skipped.  I have been trying with the NG support to connect the GF fiber jack (white box) directly to RAX120 but the internet is not getting recognized.  NG support tried with specific ip, DNS and MAC but did not work.  if this is the case, i need to return this product as well.  Anybody has connected GF fiber jack to RAX120 skipping the GF network black box, please advise.  Probably, RAX120 is not compatible with GF fiber jack and if true, any other ax router is compatible.