I've seen that OpenTTD has a universal version for macos, which can also be installed by Steam.
The Problem is that the game Starts as intel (emulated over rosetta 2) when launched from Steam. When the OpenTTD.app is launched directly from Finder, it starts in arm mode as expected. I'm not sure if this is a Steam Problem or something went wrong on your side (like packaging the old non-universal steam api... release notes).
PS: M1 MacBook Air, Steam Build: 13.10.21
OpenTTD starts in intel mode, not arm (Apple).
Steps to reproduce
Launch the game from the Steam Library
Open the Activity Monitor.app and look for the OpenTTD.app (which is displayed as intel not Apple in the Kind column).
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