Can see full active screen with all windows altough screen is locked after hibernating

Distribution

Mint 21.3 Cinnamon (and earlier)

Package version

6.0.4 (and earlier)

Graphics hardware in use

Dual graphics. NVidia GeForce MX150; CometLake-H2 GT2 (UHD)

Frequency

Always

Bug description

Scenario:
Notebook setup with 2 screens attached. The notebook screen of cinnamon is locked. After some time, the notebook goes into sleeping mode (sorry I don't know which exact level it is).

After returning from sleeping Mode, the contents behind the lock screen are shown completely (all windows on all screens) for some seconds. It even happened, that when I type my password too early, the password is written into the currently active window.

Steps to reproduce

• Connect the notebook with cinnamon to two screens.
• Lock cinnamon. (Strg+L)
• Wait until the system goes to sleep mode
• Move the mouse to wake it up again

Quite often, then the described behavior is shown.

Expected behavior

The screen should stay locked completely. It should in no case show (potentially confidential) contents from the user.

Additional information

I see some similarities to:
https://github.com/linuxmint/cinnamon/issues/11899
https://github.com/linuxmint/cinnamon/issues/11867

Start by reproducing the issue with Cinnamon locked, two displays connected, and the notebook waking from sleep, then compare the behavior with issues 11899 and 11867. Done means the lock screen remains fully opaque after wake and early password input cannot reach the previously active window.