A TCA select field with
maxitems=1 always has a selection.
It is not possible to remove it.
As soon as
size=2, you get a "x" delete button that allows you to remove the selected item.
#3 Updated by Christian Weiske about 6 years ago
Since it's not possible to have a size=1-select that has no selected option, there are only two options:
1. Make the select size 2 automatically, which allows us to remove the item
2. Automatically add a "no option selected" option that gets special treatment on saving.
Variant 2 is probably the more sensible approach. A "x" button next to the select box could add that option so that it's not visible from the start.
#8 Updated by Christian Weiske almost 4 years ago
This is fixed in TYPO3 7.6.10.
The style is broken (screenshot) because of the min-height of the dropdown, but functionality works.