I think there might be certain COPS who any queries about these issues get escalated to, as when I had to contact Monzo about something similar my query was dealt with by someone who I much later discovered, through the forum, was a senior staff member with certain broad items under his remit.
(Apols for being vague; partially this is because I don’t want to give any misinformation as my experience was a while ago now so I don’t want to assume it’d be the same for anyone else now)
After writing the about, it occured to me to search for “Monzo bereavement” and I found the following forum post from last month: When I die
Haven’t read through all of it yet, though it does confirm that so far they’ve been dealing with such queries on a case-by-case basis. It does also suggest they need a page on their website, as putting almost any other bank name in that search results with a page somewhere on their website with either a form to fill in or useful contact information.