Okay, I think this is actually due to the itch.io app sandboxing? When I launch the game from the itch.io app with sandboxing on, the Aircraft and Vehicle block previews are messed up, and the Open/Export dialogs have trouble opening some paths.
When I turn off sandboxing and launch from the itch.io app or launch the exe itself, the previews and paths are all fine. Not sure if supporting sandbox is on y'all's roadmap or not, but it'd be cool if you did as it's a useful feature from itch.