WebGPU allows using copyTextureToTexture to copy multsampled textures to other multisampled texture sof the same sample count. @shrekshao noticed GLES 3.1 provides no way to this. glBlitFramebuffer specifically disallows it

from section 16.2.1

An INVALID_OPERATION error is generated if the draw framebuffer is multisampled

There doesn't appear to be any way to work around this either as there is no way to access individual samples in GLES 3.1

So, it looks like we'll need to validate this out.