Hello,
Sorry to hear you are having issues. I tested on my system I see similar behavior with or without Start11 installed. Please refer to my video below. The Taskbar button preview stay open when I left click on it.

Few more questions.

1. Do you have any other application installed that also add or modified your taskbar and also change in Windows explorer. Such as DisplayFusion, ExplorerPatcher, StartAllBack etc.

Thank you.
Basj,
Stardock Community Assistant.

Is it possible that wallpaper engine is causing it? As a test, try uninstall Wallpaper engine and see if the issue still there.

Thank you,

Basj,
Stardock Community Assistant

Please try this, uninstall Start11, reboot immediately after uninstall done. Redownload latest Start11 version from your product download page: https://store.stardock.com/myaccount/products. Install it, reboot immediately again, retest and report back.

Thank you,

Basj,
Stardock Community Assistant

Hello again,

Did you tried my suggestion steps in Reply#5?

Thank you,

Basj,
Stardock Community Assistant

If you have Windows 11 Pro, please try the Windows Sandbox test: https://forums.stardock.com/505872/start11-support-faq#windowssandbox. See if the issue also appear while in the Sandbox.

Thank you,

Basj,
Stardock Community Assistant