Lost notes on the Android phone

My mobile phone is a One Plus 7T with Android version 11.

I used One Notes and had a lot of notes.

Then I wanted to see them on the laptop (windows 10) which I could earlier. Now I suddenly couldn't.

I tried different ways to synchronize, and then I also tried to log in and out of the One Note program on the phone. BUT now the notes are gone, disappeared?

My question is: How to restore the notes? 

(I always uses the same MS account)