The article suggest that the encrypt and decrypt should be happening in the Entity class' get/set that's in the DBcontext, which makes sense to me as to where it should be happening becuase the get/set of a class property can execute methods. The encrypt and decrypt logic is in another link on the article page.
https://www.tabsoverspaces.com/233700-custom-encryption-of-field-with-entity-framework-core
HTH