A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi CyrilTP,
After you click Site information in settings(gear)>click View all site settings>under Site Actions>click Delete this site>confirm the information>click Delete.
If you still cannot delete your sites, you can try using related cmdlets with SharePoint Management Shell.
1.Download and install the SharePoint Online Management Shell.
1)type connect-sposervice to connect to SharePoint online.
2)type the URL of your SharePoint admin center which is like https://tenant-admin.sharepoint.com
3)sign in your Office 365 account.
2.run the commands: Get-SPOSite
It will return all site collections you have.
3.run Remove-SPOSite
Note: Remove-SPOSite cmdlet does not delete a site collection from the site collections list permanently, the removed site collection is moved to the Recycle Bin. If you want to delete a site collection permanently, you can run Remove-SPODeletedSite cmdlet.
For your reference:
After the sites are deleted, check if the deleted site still exist in SharePoint online.
Regards,
Tina