Following modules are missing or built with a different engine version: Main project module

Okay, I’m fairly sure the issue was the contents of the .uproject file.

Now, I don’t know how this ended up like this, or why this broke it, but here are the only differences in the files:

Working file:

  • Has smaller indents
  • Is missing the following lines at the end, that the broken file had:
"AdditionalRootDirectories": [],
"AdditionalPluginDirectories": [],
"EpicSampleNameHash": ""
  • Has an additional property specifically for OpenXR plugins, that the broken file didn’t:
"SupportedTargetPlatforms": [
	"Win64",
	"Linux",
	"Android"
]

Make of that what you will.

I guess I’ll mark this as the solution, though this is unlikely to be helpful to anyone searching for this particular question in the future, beyond pointing out: “maybe your uproject file is weird?”.