Current State:

Currently , for "Restrict to when a field is a specific value" , the option use are Text and Number value , unfortunately Assets field value couldn't be use for this, for example, the object name/label/id or the <workspace id>:<object id> format.

 

Proposed Future State:

Support Assets field value for this conditions
 

Alternative (e.g. Third Party Plugin):

Store the Assets object name value in a text custom field ( using automation ) . Then , use the custom field value as the validator.