Yes, I checked. To clear a string type field, the action you use is to create another additional field (so that it is always empty) and write it to your field. Which is not very convenient.
Alternatively, you can put the action
https://prnt.sc/uxj66k with these settings, and after this action that clears the field
https://prnt.sc/uxj6tlThus, the field will be empty when the condition is met.