Bathroom thumbturn lock removal - no grub screws of release buttons Kitchens, doors, rails, stud, tables, chairs, stair cases, garden furniture etc... Find answers and ask questions here!

[Controversialm]

Hi, thumbturn keeps spinning so trying to remove to investigate. Can't figure out how to remove the thumbturn which is holding on the rose/backplate - there are no grub screws or release button. Please can someone review the images and let me know if there is any solution.
Thanks