As Laszlo said you must have a deleted elevation before you will see the option to restore - but it shouldn't matter how much work you have done since the elevation was deleted.
Make sure you either select the elevation group by clicking on the extent line or just right click on the extent line and you will see the option (if an elevation has been deleted already).
Selecting each of the elevations individually will not give you this option either.
You will know you have the extents selected as the black handles will be on the extents as in your screen shot.
Left clicking on the extents will bring up the pet palette which will give you the option to delete an elevation if it is showing or restore it if it is not.
You can still select the extent of an elevation after it has been deleted - the section line will be gone but the extent will still be selectable.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11