WebGL has had a number of things to note, this tickets is trying to find at least a partial solution:
•lack of support for context sharing, which means classes like OpenGLWidget is not supported (workaround is to use QOpenGLWndow)
•WebGL 2 is preferred. WebGL 1 is supported, except that legacy devices with partial or buggy WebGL 1 support won't work.
•Supporting both WebGL 2 and WebGL 1 from the same binary is not guaranteed to work: applications should choose one. Qt Quick 3D requires WebGL 2 for this reason. (we can find a workaround if someone really needs this)

Related Qt 6.8 work :
WebGL is the default in 6.8, taking its capabilities into use