Humm… yeah, it’s quite possible that the onboard GPU is being used and is therefore less capable. It’s also possible that simply switching the GPU used caused the browse to “lose the GPU context” which basically means it’s forced to do software emulation because it can’t talk to the GPU driver anymore.
If you switch GPU, I’d recommend you restart your browser to make sure it has switched to the correct driver, as it can’t do it while the browser is open.
As for the black screen… the only thing I can think of is if you use images that are larger than what the GPU can support (usually it’s 16384 pixels in either direction, but onboard GPUs, or older laptops will only support 8196 or even 4096 pixels maximum). You can check your “max texture size” limits from here: WebGL Report
I hope this helps.