Thank you everyone.
I have made an ISO of Win 10. It will install and is up to date. Win 10 update will not find any more updates, because the ISO is bang up to date..
The problem will come however maybe in the future when I try to install updates.
That's what happened first time round with my old system. I installed Win 10. Then started a cycle of installing updates. It did a few cylces, then at one point just stopped and said CPU not supported.
However I did start googling after posting here, and found there are workarounds.
When it stopped me before, it made me buy a new CPU and mobo. (8700K-rig.) While I could have continued with my old CPU, some games would have suffered. Mostly AC: Odyssey though. Origins struggled on my 4790K in busy towns. That was more down to my RAM being locked at 1600MHz though. Were my 4790K paired with an OC-board, RAM and CPU would have run faster.
I think the 4790K would have still being going by now though. Sadly it's just sat in the ASUS H97 mobo, with a Noctua UHS-12 cooler, and 16GB RAM. .. The plan was to build it into another PC, but I don't need it as yet.
Shame I felt forced to upgrade my hardware though, is what I meant. Having said that, it's been fun playing Odyssey maxed. Plus I think Div 2 might have struggled a little bit with 4790K. (Although running sync all cores might have helped.)