Strangely, I can not reproduce your issue on my system. Secondary monitor vertical taskbar can be resize accordingly. Perhaps something not properly get install. Please try, uninstall Start11, reboot immediately (important), download latest version available in your account product download page: https://store.stardock.com/myaccount/products. Install it, reboot immediately again. Retest it and report back.
If the issue still there, we need more information on your system.
- Windows 11 full version and OS Build numbers. Use Winver.exe to get these numbers.
- Start11 full version installed.
- Do you have any other application that also manage your taskbar/Start menu/Explorer. Such as StartAllBack, ExplorerPatcher, OpenShell etc.
Thank you,
Basj,
Stardock Community Assistant