root wrote:

HDMI signals go from a source to a display. I need a device
to go between the source and the display. This device would
save the edid of the display and report that back to any
source connected to the device whether or not the display
is on.

somde KVMs work that way, but you'd probably find it difficult to get
info to confirm it for any given model, before buying.

One response to a previous query of mine suggested a device
that costs about $100 which is too much for my application.

This will do it, about half of the price, check for local suppliers

https://cpc.farnell.com/sy-electronics/sy-edid-master/edid-master-dongle-manipulates/dp/AV28015

What would such a device be called so I can google for online
options?

EDID emulator