i can't help with game suggestions but i just wanted to say, well bloody done to your dad at 83 building a pc. i wish him many more years of good health to enjoy.
Needed some help with the software setup, and the first motherboard and 4090 needed to be RMA'd, thankfully I could be with him for those bits, but the vast majority he's done himself. We built "our" first computer together probably over 30 years ago now, a trusty old SX25.
Horizon was another I was considering, but dodging attacks, and shooting moving targets may be tricky. Might suggest them though.
Definitely looking more at management style games I think. I see there's a new Settlers coming soon, will have to recommend that to him, Settlers (the original) and Gauntlet, were two games we used to play together when I was a kid.