I opened OneNote Online (E3 Plan) in the Opera Browser 51.0.2830.34 in private mode. Then, I got the welcome popup, as shown in the screenshot below.
The word Überspringen is overlapping the button. I am unsure, if it's a language Issue, maybe a layout problem; so I hope it's ok to report it here.
Note: I could not reproduce it in another browser (in private mode), as I did not get the screen again. Also in Opera, a second time, I open One Note, the screen is gone. Deleting cookies and so on does not let the welcome screen reappear too.