When clicking at the main part of the 'Freeze Rows and Columns' split button in Calc's main toolbar, the rows and columns above/left of the selected cell will be freezed. This is the default option.
When clicking at the arrow of the split button, then options for only freezing first row or column will be shown in a drop-down menu.
I think this is not the optimal behavior of the split button for users. (But I didn't find UX advices for that .)
It should be possible to switch also to the default option inside of the drop-down menu. Otherwise there are 2 different behaviors within the split button: Default option only by clicking the main part of the split button. Other options by selecting the drop-down menu after clicking at the arrow.
If the user isn't sure what is needed, it should be possible to also select the default option. Otherwise the user has to go out of the split button's drop-down menu and has to click on the main part of the split button again. It's not possible to click at the default option when the drop-down menu is open.
Add default option in split button for 'Freeze Rows and Columns' at the first position in the drop-down menu.
I would say this is a useful idea. :) !
It's the usual behavior of splitbuttons. Another example is Save with Save As and a couple of other options underneath it. So my take: WFM.