Qt Creator suddenly unable to run application due to "Could not find the Qt platform plugin"

[wdm3]

I am on Windows 10 64-bit. I installed Qt 5.15.2 and Qt Creator 10.0.2 via the online installer. I was able to open a project in Qt Creator and successfully build and run it. However suddenly the application no longer successfully launches from Qt Creator. I get this error message upon launch:

This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

The above error also appears when I try running the .exe directly from Windows Explorer.

And this appears in application output of Qt Creator:

14:54:53: Starting C:\git\build-QVproject-Desktop_Qt_5_15_2_MSVC2015_64bit-Release\bin\QuickViewer.exe...
5
qt.qpa.plugin: Could not find the Qt platform plugin "windows" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

14:54:58: C:\git\build-QVproject-Desktop_Qt_5_15_2_MSVC2015_64bit-Release\bin\QuickViewer.exe crashed.

I am not sure why this error suddenly started happening. I uninstalled and reinstalled Qt and Qt Creator and the issue is still occurring. Any ideas why this could be happening?

[SGaist]

Hi and welcome to devnet,

Did you run windeployqt before trying to start it outside Qt Creator ?

[wdm3]

Thanks, that resolved the issue. After running windeployqt, the exe now launches successfully from both Qt Creator and Windows Explorer.

[SGaist]

You shouldn't need to do that when starting from Qt Creator after a clean build.