I don't know when it started (after 1.21.0 included for sure), but I can't connect anymore to my Microsoft account correctly...

The signing status on the main menu is always stuck on "Signing into Nintendo Account..."

I tried to reset my game, and without connecting into a Microsoft account, the game works as expected.

If you sign-in into a Microsoft account, for that session it will work fine (except for skins that won't load), but after restarting the game, the issue reapers.