Unable to delete section group in desktop app or web browser

Dear @Eszter Mihaly,

Good day! Welcome to Microsoft Q&A forum!

Regarding this situation, I tested this on my end by creating a section group in OneNote and was able to delete it successfully, so it does not appear to be a general issue with the feature itself.

I created 3 sections (Section 1, Section 2, Section 3), then created a new Section Group with Section 1 and Section 2 by moving them into the section group.

I then right-clicked the new Section Group > Delete > Yes

After that, the Section Group was deleted and moved to the Deleted Notes

Therefore, to help narrow down the cause, could you please confirm:

• Is the notebook stored in OneDrive for Business or SharePoint, or is it a personal notebook?
• Are you the owner of the notebook, or was it shared with you by someone else?
• Does the issue occur with only this section group, or with any new section group you create?

In the meantime, could you try the following:

• Create a new test section group in the same notebook and check whether Delete when right-clicking a Section Group is available
• Make sure the notebook has finished syncing and then restart OneNote
• If the section group contains sections, try moving those sections out of the section group first, then attempt to delete the now-empty section group

If possible, a screenshot of the notebook structure and the grayed-out Delete option would also be very helpful.

I appreciate your time and look forward to your update.

Thank you for your time and patience.