I just saw your post on reddit and responded to you there before seeing this post.
I’m copying my response here as well in case someone else stumbles on it with a similar problem:
The error is the one appearing in the last line of your screenshot :
Metadata validation failed for world “tod-new”: The file “lang/en.json” included by world tod-new does not exit
I’m not sure how you created your world, or where you imported it from, but somehow, it’s referencing a language translation file inside the world which doesn’t exist and Foundry refuses to recognize the world as being valid because of that.
Add an empty file named ‘en.json’ inside a ‘lang’ subfolder inside your world
Edit the ‘world.json’ to remove the reference to the language file (you’d need to understand the world.json file format to avoid breaking it further)
In either case, you’ll need to export your world, edit it locally, then re-import it via the Import Wizard.
I see from the Reddit thread that you’ve already updated your modules but still ran into the issue. The UI disappearing does sound like a module-related issue. If you’ve fixed the file validation issues then we can move on to trying to fix the modules
The file “lang/en.json” included by world tod-new does not exist
I’d recommend installing Module Compatibility Checker on the v9 backup you currently have installed and checking to see if everything is actually v10 compatible. For some of them that don’t have v10 versions, you’ll need to disable them or use an alternative module if they exist.
Make sure you take a v9 backup, and when you’re ready, follow the update guide to v10
In brief, you’ll need to
Set your Foundry server version to v10
Visit the Bazaar and update systems and all modules to v10 versions. Some modules might not work in your world, if they only support v9. You can ignore or disable those.
Try to launch your world in v10. It’ll disable modules and do a migration. Once the migration is complete, you can start activating modules. If you run into problems, double check that those modules are updated to v10 versions, or disabled if they don’t have a v10 version
That should get you sorted. If you have any trouble, feel free to join us in Discord and make a ticket in #ticket-support and post an invite to your game, and then perhaps someone can hop in with you to help real-time