• If Qt is not installed yet :
  → Go on qt.io then get qt (you can go towards open source qt, then download the online installer)
  → Once done, lauch this installer, when your in the Select Component step, choose to configure your installation manually, then select the component Qt x.xx.x>MSVC 2019 32-64bits (depending on the version(s) you want).
  → Open VS2019. Go to Extensions>Qt VS Tools>Qt Version then add the path to the msvc qmake (for exemple : C:\Qt\Qt xx.xx.x\msvc2019_64\bin\qmake.exe).

• If Qt is already installed :
  →Go (with explorer) in your Qt folder
  →Launch the maintenance tool MaintenanceTool.exe
  → Add Component then select Qt x.xx.x>MSVC 2019-32/64 bits then click next
  → Open VS2019. Go to Extensions>Qt VS Tools>Qt Version then add the path to the msvc qmake (for exemple : C:\Qt\Qt xx.xx.x\msvc2019_64\bin\qmake.exe).

Hope it helps.