@MightyHandy 

This is how it will work.

1. Configure Netgear router in router mode (not in access point mode);

2. Set it with its own SSID and IP range, different from Deco mesh;

3. Connect Netgear router WAN port to Satellite Deco port with Ethernet cable. Makes sense to do that with Satellite Deco closest to Roku;

4. It is recommended to place Netgear router at least 6ft (2m) away from Deco it is connected to, to avoid WiFi interference between them both;

5. Connect Roku to Netgear SSID.

I happened to have older Roku model, one with infrared remote, but I tested similar setup and it did work. Roku just connects to the Internet, it does not care if it has to go through two different routers to get there. Nothing connects to Roku, meaning that setup should not cause any issues with inbound connections through Netgear router - there should be none.

Hint: find "allow management access from the Internet" or similar setting in Netgear router and enable it. After that, you can manage Netgear router from the browser on any device in your home network.

@Alexandre. Hmm, is this the only option?  So you're saying you basically need to double NAT this.  Ensure that none of the MAC addresses are on same LAN.  And keep all IP addresses off of the subnet entirely.  Basically fully isolate those Roku's into their own cocoon.  Does this mean Deco can't handle having another AP on the same LAN?  With that level of isolation I'm wondering if Roku's advanced features will even function anymore (Alexa integration, Roku App, Streaming content from Plex, etc.)

If I just put the router in AP Mode it would be way easier, and I wouldn't lose capabilities.

@MightyHandy 

It appears you are utilizing Roku more than I do. All I need from Roku is stream Netflix or YouTube on TV. 

Yes, router should work with Deco if you configure router as wired access point. I am assuming you understand what you are doing, for example you will connect Ethernet cable coming from Deco to LAN port of router, not WAN port.

We have 4 Roku's (2 TCLs, 1 Ultra, 1 Streaming Stick), sadly they are positioned in the exact same entertainment centers as the deco nodes. And the interference they generate is substantial. Moving them all onto a separate AP would let me control what channel they all use to keep it far away from Deco. But, that really only works if its acceptable to have non-Mesh AP's on the same LAN as the deco.

The underlying mechanism that Deco is using is totally secret/proprietary. So, I can't tell if this would completely break the Deco Mesh's ability to keep track of what clients are where. Or, if it would all work without a hitch.  Like would it attempt to steer/roam assist clients of the non-deco AP?  Would it get confused thinking those clients are wireless and part of the mesh?

I really don't want to put that AP in Routing mode if I can help it. It would create some crazy complexity in allowing rest of network to interact with Roku's. But, it would also create a little bit of a wiring nightmare, as I was essentially going to replace my unmanaged switch with the AP. That is not possible if the AP is in routing mode.

@MightyHandy 

MightyHandy wrote

We have 4 Roku's (2 TCLs, 1 Ultra, 1 Streaming Stick), sadly they are positioned in the exact same entertainment centers as the deco nodes. And the interference they generate is substantial.

In that case, there is one more option to consider: wired connection. Roku Ultra has Ethernet port - wire it to nearby Deco unit with Ethernet cable. Check if your Roku TCL TVs have Ethernet port, and wire them to their nearby Deco units, too.

With a bit of luck, i.e. Ethernet ports availability on Roku devices you own, you may end with just Roku stick connected wirelessly, and that is quite smaller problem to deal with.