Thanks for the clarification.
I'm having trouble getting it working, but I'm not yet sure what part of my system is the problem.
To be fair, I don't otherwise use the VGA out on my I/O card (so I never saw it 'working'), and I also had a problem (with slightly different symptoms) with the composite adapter from Antonia Villenas. The difference being that your board requires a male-male VGA cable.
I'm using this one:
https://www.amazon.ca/gp/product/B07JQ1M7MW
I got the IO board from MisterAddons.com, so I wasn't expecting it to be that (although anything is possible).
I'm going to continue running some tests before asking more questions; I now have an additional DE-10 and will receive another IO board in a couple of days, so I'll basically have two of everything and can be more thorough in analyzing what's happening.