Specifically, Can Windows 10 Pro use 3 (1 ethernet 2 WiFi) at a time?
Yes, I just tried it out.
How? Using “Bridge Connections”?
I literally just connected to two of my three networks on two WiFi adapters while the wired ethernet was already on the third network. Windows took care of all the details automatically.
That way it would not use all 3 at a time
Yes it does, I can connect to devices on all three networks simultaneously.
FYI I do two at a time connections on a nearly daily basis for my engineering work.
If you connect to 2 networks then go to Networks & Internet Connections/Status will show only one network
Do you really need 3 per time?
Not on my Win10 Pro workstation, it shows all networks.
As I said I do the two simultaneous connections on a nearly daily basis.
I have no idea why it doesn’t work for you.
I just dawned on me that perhaps you are not using non-overlapping IP address ranges. Each network must have a different range, on my three networks the ranges are 192.168.1.x, 192.168.2.x and 192.168.3.x all with net masks of 255.255.255.0.