Can’t make new reminder in Mail Rule

I’m trying to create a Mail Rule that makes a new reminder whenever I get a payment notification from my internet provider. This AppleScript works when run directly or as a step in a Keyboard Maestro macro:

use AppleScript version "2.4" -- Yosemite (10.10) or later
use scripting additions

set remName to "Xfinity bill"
set remNotes to "https://customer.xfinity.com/#/billing"

tell application "Mail"
	set selectedMsgs to the selection
	repeat with theMsg in selectedMsgs
		set msgDate to date received of theMsg
		set remDate to msgDate + 5 * days
		set hours of remDate to 10
		set minutes of remDate to 0
		set seconds of remDate to 0
		tell application "Reminders"
			tell list "Expenses"
				make new reminder with properties {name:remName, remind me date:remDate, body:remNotes}
			end tell
		end tell
	end repeat
end tell

It creates a reminder in the Expenses list with the “remind me” date I want.

Of course, I don’t want to run this by hand; I want it run automatically through a Mail Rule. But setting a Mail Rule to run this nearly identical script fails.

use AppleScript version "2.4" -- Yosemite (10.10) or later
use scripting additions

set remName to "Xfinity bill"
set remNotes to "https://customer.xfinity.com/#/billing"

using terms from application "Mail"
	on perform mail action with messages theMessages
		repeat with msg in theMessages
			set msgDate to (get date received of msg)
			set remDate to msgDate + 5 * days
			set hours of remDate to 10
			set minutes of remDate to 0
			set seconds of remDate to 0
			tell application "Reminders"
				activate
				tell list "Expenses"
					make new reminder with properties {name:remName, remind me date:remDate, body:remNotes}
				end tell
			end tell
		end repeat
	end perform mail action with messages
end using terms from

Through some judiciously placed display dialog commands, I can tell that it fails when it tries to make a new reminder.

I suspect this has to do with privacy and permissions in Catalina. I opened the Privacy tab in the Security & Privacy preferences and tried to give Mail permission to access Reminders. But there’s no obvious way to add an app to the list.

As you can see, there’s no + button for adding an app. Dragging the Mail.app icon from Applications to the list doesn’t work, either.

Googling has led me nowhere. What am I missing?

Welp, I guess there’s no direct solution. My indirect solution is to move the emails to a special mailbox and set up an AppleScript to run periodically and create the reminders.

Sad to lose a simple and longstanding automation technique.