Hi there, @yohannh,
It still displays By [author’s name] and the date at the top of the pages of the lessons even when unchecked.
If the Display Lesson Author:?Output the Lesson Author on Course single page & Lesson archive page.
option is unchecked on Sensei LMS > Lessons > Settings, then it’s possible that there’s a conflict between a plugin or the theme.
Can you try to switch your theme to Twenty Twenty temporarily and see if the problem persists?
If the issue persists, please temporarily deactivate all your plugins (and keep Sensei enabled) and check if the problem gets fixed that way. If it works, then reactivate each plugin individually to find out which is causing problems.
Let me know how you get on!