With switch to QtWebEngine, there were unfortunately issues with packaging all required files for Windows. As a result, on some Windows system new version of QupZilla didn't work at all.
It should be all fixed now, please re-download the installer (or portable) from homepage again. I apologize for any inconvenience this may have caused.
Note for Windows XP: You may see warning popup messages on startup, it can be fixed by removing D3Dcompiler_47.dll in directory where you installed QupZilla.