Dave Plowman wrote:

I have cabled LAN, Wi-Fi and a Wi-Fi range extender.
If any two are on say the same Wi-Fi, they share files normally. But I'd
not need an extender if this covered all the house. With one on the main
router Wi-Fi and one on the range extender (TP Link), can't share. Same
when one is on the cable LAN and another on Wi-Fi.

Before even thinking about file shares ...

Do you have a single IP subnet that spans all three physical media?

A single DHCP server?

Does your router act as a local DNS server or just as a forwarder to an
external DNS server?

Can every PC ping every other PC regardless of what they're connected
to, by IP addr? by name?