Complex sentence: Traditionally, each subsequent monarch has agreed to this formality as part of the ritual of their accession: although they no longer have any actual right to revenue from the Crown Estate as they no longer govern in person.
Split into simpler sentences: Traditionally, each subsequent monarch has agreed to this formality as part of the ritual of his or her accession. The monarchs no longer have any actual right to revenue from the Crown Estate as they no longer govern in person.