RBR750 - how do I force devices to connect to a specific router or satellite? Or split networks?

Some suggestions:

Netgear has a community forum specifically for the new "AX" series of products:

https://community.netgear.com/t5/Orbi-AX/bd-p/en-home-orbi-ax 

People who participate in that forum are more likely to own an AX product and be familiar with how it functions than those of us in this forum who have the older product.  You may be more likely to get an informed response by posting over there.

Some additional detail may be useful.  For example, "communicate directly with my PC" is confusing.  "Directly" as in "not going through any sort of network"?  My printer offers a feature where it sets up a WiFi access point of its own and devices can print directly to it without going through a network, but I am not familiar with PC programs doing that.  Maybe identifying the program would allow others to research this requirement in more detail.

How was the conclusion about "splitting the SSID's" reached?  Every device that I have can connect to every other device on my network, irregardless of which WiFi band it is connected to.  That is the whole purpose of having a network.  I have vague memories of reading that the AX products do not support the "hack" people use on the older Orbi's to split SSID's, which is another reason to post over in that forum because I honestly pay little attention to the AX product (since I don't have one).