Editable whiteboard limit reached though no whiteboards exist in “my account”

When trying to create a new whiteboard I always get the message that I have reached the limit of editable whiteboards.

A check for existing whiteboards shows that there are no whiteboards in my account.

The message even shows the name of a whiteboard dated in 2023, which I can’t find.

All existing whiteboards should be deleted so that I can start from scratch with 3 new editable whiteboards.

I need the functionality and should be able to use it with my basic account.