Hi @GAK ANAGROVA Vera,
Thank you for posting on the Microsoft Q&A forum.
Based on your description, it sounds like the permissions on the SharePoint site or list may have been changed in a way that removed the owners who could manage access. Since you can no longer edit the list settings or create new lists, I would recommend contacting your organization's Microsoft 365 or SharePoint administrator for assistance.
Ask the administrator to:
- Open the SharePoint Admin Center.
- Locate the affected SharePoint site.
- Verify the site's permission settings and owner group membership.

- Add your account back as a Site Owner (or grant equivalent permissions) so you can manage the list and site again.
If there are no remaining site owners with sufficient permissions, a SharePoint administrator should still be able to restore the appropriate access from the admin center.
To help narrow this down further, could you confirm:
- Is the issue affecting only this specific list, or all lists on the SharePoint site?
- Did the permissions change only on the list, or were changes also made at the site level?
Thank you again for your time and understanding. I look forward to your update.