Can Targetb Display mode on suitable iMacs be used with PCs? or with a hub of some kind? It works fine with my MacBook Pro but i want to connect with my work Laptop to get a second screen

No.

carefully read > https://support.apple.com/en-us/HT204592

Many thanks

I read that article before posting (and carefully)

Is this where you get your answer?

I was hoping there was something undocumented…

Disappointing that iMac can take Thunderbolt video input only from another Mac, but I suspect that’s it, as you say

Many thanks

The iMac is a computer, not a display for a PC or Gaming system.

For a short time some models supported TDM, but it is no longer supported.

Yes I spotted that

I will have to endure Citrix on the MacBook+iMac or else buy a second monitor for the PC Laptop

Yeah’ if you had a decent external display, then you could use it as a second display for the PC and/or either Mac.