@SimpleMan_Auz 

Hi,

I am not sure if connecting other antennas to the AX11000 would solve the problem.

If the router was placed near a window and the cables to the antennas were really short, then it might work. But if many meters of coax cable were required from the antennas to the router, then the higher gain of Yagi antennas might be offset by the higher impedance of the long cables.
Besides, the AX11000 is a 12-stream wireless router. Since apparently only 8 antennas are external, there must be 4 more antennas inside the housing, which could turn out to be the one's used for the connection the camera requires. Also there is no way for the user to control which antennas of any band are used at any given time to connect to a certain client device, so the whole thing would only make sense if all 4 antennas belonging to the same band are replaced with high gain antennas.

A better option might be to get an access point with already built-in directional antenna(s) and whose Wi-Fi specifications match that of the wireless camera.

Do you have the exact Wi-Fi specifications of that 4K Wi-Fi camera at hand? (i.e. 2.4 GHz single-band or 2.4GHz/5 GHz dual-band?, one or two or more antennas?, 802.11ac or 802.11ax wireless standard?)

As far as trees in the line of sight are concerned. Even trees can affect the transmission of signals in the 2.4 GHz and 5 GHz range substantially.