There is a Registry setting, provided by Stardock, available for disabling the taskbar previews.
Create a new String in HKEY_CURRENT_USER\SOFTWARE\Stardock\Start8\Start8.ini\Start8 and name it S11_HideTBPopups and set the Data Value = 1
All values are REG_SZ (string) type. Create the key with the specified value to enable the feature.
After manually editing registry keys, run Start11Config RELOADSETTINGS from a command prompt to apply changes or Restart Explorer.
Follow this link to the Support page where this change is located.
https://support.stardock.com/space/SHC/1750138994/Start+Menu+Products+Registry+Settings#Taskbar-Options
NOTE: You will need at least Start11 v.2 version 2.6.0.2 for this to work.