World is gone after downgrade

I had to downgrade my Foundry account due to funds, and now I can’t see my game / world.
It was a custom world based on D&D 5E. I have NOT upgraded to D&D 3.0.
It was there when I downgraded, as I spent time making sure I removed unnecessary assets and that it still worked, however, I was under the asset limit for the downgrade anyway.
All the assets are still in the assets library, and if I look at the save points I can see my world, however, because I downgraded I can’t restore from the save.

Weirdly I can see an older world I ran ages ago I believed I deleted.
Can you only have one game world when you downgrade?

For what it’s worth I’ve updated my subscription, enabled the game manager, and the game is available. wipes sweat
How do I make it the default game for when I downgrade?

You most likely had lost access to the Game Manager feature of the Forge when you downgraded, and you should have received a notification that lets you know about it as well, when the downgrade occurred.
Without the Game Manager, then you’d need to use the normal Foundry behavior for accessing worlds. Once you’re in your Foundry server, you’d need to click the “Return to Setup” button in order to access Foundry’s setup menu which has the world selection screen. The reason you saw an old world when you launched your Foundry server was probably because that was the last world you launched through Foundry back when you were using the Forge without the Game Manager option enabled.
You can read more about it here: The Game Manager - Docs - The Forge
I hope that helps.