Especially a fork called JGR's patchpack, featuring programmable signals and so much more.

OpenTTD's default signaling system is mediocre. "Path signals" which are "recommended" and the only signal system not locked behind a settings change, will get you into trouble more often than not. You can only put a path signal somewhere where "it is safe for an arbitrary train to park here", which is a problem more often than not. If you are used to block signalling, as used in real trains, path signals will repeatedly surprise you in unfortunate ways. You have to basically deprogram everything you learned about signalling and even build rather different track layouts to use them. Add to that, platforms are not integrated into path signals in any useful way, so a train will sometimes refuse to advance to it's destination platform if it is a "Drive through" capable station if it cannot reserve a path well past it's desired endpoint.

IMO block signals are much simpler to understand for simple use cases, even if it is hard to make complicated railways with them. I think for normal people picking up OpenTTD, they would be a better choice.

Is it Sweet Transit? The about section mentions that the developer was part of Factorio.

Edit to add link - https://www.sweettransitgame.com/

He was one of the graphics contractors not a dev.

It is not very good. The game design is just and, failing to be either a good train sim or an interesting strategy game.

It basically flopped in early access.