Can't enter XR mode

Questions
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1

Hi, all !
I am completely stucked on strange error, while working on my present project (GemView):

[Immersive Web Emulator] native WebXR API successfully overridden (repeat 3 times !) 
webxr-polyfill.js:27977 Uncaught TypeError: canvas.getContext is not a function

so, I can’t enter XR mode.
Three.js version is “0.169.0”, all examples are working, can’t figure out what I am doing wrong, any help please !

Thanks in advance.