eyebo says:
I think I've fixed the link with your Ubisoft account. So you shouldn't see the error anymore.
However, to get the tracks you've built on PS5, you'll need to access them through https://www.trackmania.com
Then you can download them on PC and upload them here on TMX.
Having your Ubisoft account linked does allow you to mark maps as favorites here on the site, and then you'll be able to find them in your favorites in-game.
I hope that helps.