Hello guys. I’m new here. Wanted to ask though if it’s possible to create procedurally generated terrain in GDevelop. You know, something similar to the one in Alto’s Odyssey.
Hi and welcome. 
Sure, you can spawn terrain and any game elements while playing, all is a matter of actions (what to do) and conditions (when to do it).
Take a look at some game examples or tutorials to see how they’re done. There’s an Endless runner tutorial for instance. If there’s something you can’t understand, check the wiki.