Managed to fix this by:
- Installing Direct Play : go at "Control Panel">"Programs and Features">"Turn Windows features on or off">"Legacy Components" and check "Direct Play" to install it.
- Setting MotoRacer.exe, game.exe, and the Launch Moto Racer shortcut to run in 16 bit reduced color mode, forced 640x480 resolution, and run as administrator through properties.
There might be a better way to do it, but this is the only way I've managed to run it. Game just crashes when launched through GOG Galaxy for whatever reason.