my thunderbird folders has disappeared

seeing some sort of connection error?

What mail provider are you using?

my folders was okay in the evening, but next morning they were gone. I am connected to Microsoft 365 so all mail goes through there, my folders show on their end. They know nothing about Thunder bird. Which connection errors are you thinking about ? I am not very experienced with IT. How would I check ? I hope you can help. I am having my connection through Plus net. Kind regards hmm1