Adobe Flash Player has been retired because of security issues.
If you try to install Adobe Flash Player on Windows 10 or 11 you will get an error message.
But if you only want to display the PTBSync flash clock on the desktop there is no security risk.
PTBSync loads a locally installed flash file into the Internet Explorer API which displays the desktop calendar.
Then copy the content of the folder "Windows" in the ZIP file into C:\Windows (2 subfolders).
Then double click the file Registry.reg in the ZIP file which registers the OCX files in the registry.
After enabling the Template_Calendar_Clock_Flash in the PTBSync window "HTML Desktop / Print Calendar" you are ready.
Here you see a screenshot of the PTBSync Flash Clock running on the Windows 11 desktop: