I have configured workday like so, and it seems to be ok according to the log.
2023-07-10 10:46:30.971 DEBUG (MainThread) [homeassistant.components.workday] abort_check in options with {'name': 'Workday Sensor', 'country': 'DE', 'excludes': [], 'days_offset': 0.0, 'workdays': ['mon', 'tue', 'wed', 'thu', 'fri'], 'add_holidays': [], 'remove_holidays': [], 'province': 'NW'}
2023-07-10 10:46:30.988 DEBUG (MainThread) [homeassistant.components.workday] Found the following holidays for your configuration:
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-01-01 Neujahr
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-04-07 Karfreitag
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-04-10 Ostermontag
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-05-01 Erster Mai
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-05-18 Christi Himmelfahrt
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-05-29 Pfingstmontag
2023-07-10 10:46:30.989 DEBUG (MainThread) [homeassistant.components.workday] 2023-06-08 Fronleichnam
2023-07-10 10:46:30.990 DEBUG (MainThread) [homeassistant.components.workday] 2023-10-03 Tag der Deutschen Einheit
2023-07-10 10:46:30.990 DEBUG (MainThread) [homeassistant.components.workday] 2023-11-01 Allerheiligen
2023-07-10 10:46:30.990 DEBUG (MainThread) [homeassistant.components.workday] 2023-12-25 Erster Weihnachtstag
2023-07-10 10:46:30.990 DEBUG (MainThread) [homeassistant.components.workday] 2023-12-26 Zweiter Weihnachtstag
When I do any changes, for example adding a holiday;
The following happens.
2023-07-10 10:52:05.758 DEBUG (MainThread) [homeassistant.components.workday] Errors have occurred in options {}
2023-07-10 10:52:06.822 DEBUG (MainThread) [homeassistant.components.workday] abort_check in options with {'name': 'Workday Sensor', 'country': 'DE', 'excludes': [], 'days_offset': 0.0, 'workdays': ['mon', 'tue', 'wed', 'thu', 'fri'], 'add_holidays': ['2023-07-10'], 'remove_holidays': [], 'province': 'NW'}
For today, 2023-07-10, the state of the workday sensor is On, which it shouldnt be.