How to include List-Unsubscribe-Post header in DKIM signature?

As per RFC 8058 and newest policies by Google and other big players, it is practically mandatory to have DKIM signatures that cover also the List-Unsubscribe-Post: header.

Unfortunately, my UTM 9.718-5 does not do so, though it does cover List-Unsubscribe: and several more headers out of the box.

Is there any way I can tweak it to also cover the List-Unsubscribe-Post: header in its DKIM signatures?