Good afternoon. There are several settings in the universal block field settings
https://prnt.sc/XedZIiI0IWkothe first "Required" - if the field has no value, an error will be issued when saving
second "Required to be filled in" - opens the field for editing if there is no value there
they work regardless of the display of the block
As I see, the edit box is open. If you still need an error when saving, is it possible to put a second check mark?