Windows 10 Pro 20H2 Build:19042.928
Windows Feature Experience Pack 120.2212.551.0
WindowBlins 10.87 (before to ask here help)
I have uninstalled WindowBlind and Start10 then i have rinstalled WindowBlinds...from a setup of previous version 10.7 (if i not remember wrong, and setup come from HumbleBundle). Then before to apply any theme i have updated WindowBlinds to 10.87, applied a theme and the problem is fixed. Also with Start10 i was struggle with application search bar that wasn't working. Now Start10 and WindowsBlinds seems to work fine.
Sorry if i wasted your time, but before asking here i have tried to reinstall and restart my pc several times without success...thanks anyway!