It seems that you are unable to add or remove columns in a SharePoint list or library. Here is a list of potential solutions which could help you address this issue:

1. Check the design mode settings of the page.
2. Check the default view settings per page.
3. Check the permissions to edit the list or library.
4. Check the versioning settings in the list or library.

If the above solutions do not work, then please seek out additional support from your systems administrator or contact SharePoint Support directly.