Mail Flagged count : why can't Apple get this to behave?

I have an M2 MacBook, an M4 iPad and an iPhone 15 Pro. One single iCloud mail account that I've had since it was called MobileMe, about 25 years now.

And yet, when looking at the count for the Flagged folder, my devices almost never agree, nor are any of them usually correct. In 25 year, they've been aligned and correct for a total of about 7 minutes.

I've tried relaunching all apps, rebooting all devices, logging out of and back into iCloud (a total PITA) at least a dozen times over the years, with little or no satisfaction. iCloud.com Mail doesn't have a Flagged folder, so I can't look there for any arbitration.