Choose "generate new OpenPGP key" in Kleo. In the advanced settings click on the drop-down arrow next to the date. Choose "Today" in the dropdown.
OK + OK for "Generate key".
Result: General error.
gpg debug (no surprise):
4 - 2023-06-09 13:33:45 gpg[3544]: -&16:8: invalid expire date
Please remove the option "Today".
Additionally it should not be possible to click on the current date in the date-picker.
And if the not allowed date is typed instead, it should be ignored and the displayed date set to the next possible valid date.
See T6479 on key extension, too.