Well, you got halfway there by adding the male tag to your post. Just looking through all the projects with the male tag brings up 169 threads. Sure, not all of these will be exclusively male weight gain, but there’s still a fair few to choose from.
I was going to mention a few off the top of my head, but Fenrir already linked them. If you’re fine with inflation though, I do know of pumpt. A bunch of other male-focused games were also linked in this thread.