QtQuick Item.layer not working with WebAssembly

In QtQuick, I was trying to apply a ShaderEffect to an Item tree by using the Item.layer feature. The WebAssembly application however only shows a blank rectangle / empty texture.

The problem is already triggered by just enabling offscreen rendering  using "layer.enabled: true". The Firefox console is filled with the following type of message pair:

Error: WebGL warning: clear: Framebuffer not complete. (status: 0x8cdd)
Error: WebGL warning: clear: Framebuffer must be complete.

Looking up the status code emitted by the Browser:
FRAMEBUFFER_UNSUPPORTED 0x8CDD

Chrome keeps repeating another error description:

WebGL: INVALID_FRAMEBUFFER_OPERATION: clear: conflicting DEPTH/STENCIL/DEPTH_STENCIL attachments