Home Network problems with Internet

Large home network of 6 Windows 11 PC’s. One Pc drops internet connection periodically when the machine is left idle. It does NOT drop the LAN. Other machines not affected. I have tried :-
7 different NIC cards and 4 wireless adapters.
All power/sleep settings left “open”
Many , many settings and ideas from the web
Countless updated drivers
6 Complete software rebuilds on 2 different “C” drives
3 Routers and 2 different ISP’s

It just started out of the blue one day and nothing seems to make a difference. It has been going on for months.

If anyone knows how to think outside the box, you could restore my sanity.