The reason I asked was because in your first post you said " the "whole home wifi" app stopped working with my equipment", The Complete Wi-Fi discs should be configured using the My BT app not the WholeHome WiFi app.
As far as I am aware, they do form a mesh but I've never really looked into it and can't be sure
See message 4 of this link
Its quite straightforward, both are mesh systems, Whole Home (white discs) are able to be used with any ISP or router and form their own mesh independently of the router. Complete WiFi (black discs) can only be used with the BT Smart Hub2 which integrates as part of the mesh with the discs.