Hi François,
To investigate the issue, we would like to confirm the following information:
- Are you trying to delete a classic SharePoint site or Office 365 group site?
- Did you try deleting the site from browser? For detail information, please see Delete a SharePoint site or subsite.
- If there’s another owner of the site, please check with him/her if they can delete the site from browser or using PowerShell command.
- When you try to access the site from browser, you get 404 FILE NOT FOUND error. Correct? Could you please provide the complete screenshot?
Thanks,
Neha