Entity reference fields store the ID of the referenced entity. They don't store anything else about the referenced entity.
You have an Entity reference towards nodes and the data that the ER field stores is the node ID. That is why when you add a filter for that ER field you get the "number" options, because the ID is a number/integer.
But there is a way to add a filter that filters results based on other properties of the referenced entity. When you need extra information you add the Relationship based on the ER field. This introduces all other available info about that entity into your Views.
In your case, you want to add the Relationship for your ER field (
Content referenced from fiscal_certificates). Require it if you only want results that don't have that field empty.
After you add the Relationship you can add the
Title filter, but make it use the Relationship for the ER field. Title is a text field so you'll get the text options (Contains...).
If you don't use a Relationship on that filter it will search through Titles of your "original" items, but if you use the ER Relationship it will search through the referenced node titles.