I started on Muluna with a friend but we are unable to automate heavy trucks there. When clicking on it it only shows the inventory instead of the train menu.
I set Any Planet Start to none, created a new game in sandbox, placed down a truck and it worked. Swapped surface to Muluna in editor and the issue is back. I'm not sure what is causing the issue, so I'm not sure what else to provide you here. Hope I can help you resolve this, the trucks are super cool to use.

Thanks for the detailed report, that made it easy to find! Muluna swaps every fuel-powered vehicle for its own Muluna version (so it runs on oxygenated fuel), and the autopilot doesn’t recognise that version as a truck yet, so you only get the normal inventory. I’ll fix it in the next update so trucks work the same on Muluna.

Oooh , of course! I was actually wondering why the truck entity was saying muluna as source, instead of the string of mods it normally has. Thanks for the quick fix!