Delete photos from Messages info window on Big Sur fails
This question has been asked many times in different incarnations, but I have not found an open thread.
To reduce storage on iCloud, I need to delete photos and attachments that are stored by/for Messages.app. My Macs are running Big Sur 11.6.1, and "Messages in iCloud" is enabled (to allow automatic sync between iPhone (iOS 15.1), iMac and MBP). In Messages, I select the person/conversation and click the "i" in the upper right corner. This opens the info screen, I scroll down to the Photos section, right click on one Photo or attachment opens the menu which offers "Delete". A confirmation screen pops up, and after confirming "Delete Attachment" the selected photo should be removed (ideally for all devices that are in sync via iCloud).
However, I have quite many photos that simply stay, not matter how often I try delete.
Any suggestion what to try?
Clicking the button "Sync now" in the iMessage Preferences does not help.
MacBook Pro 15″, macOS 11.6