Two things:

The door did not have a "plate glass window" as you have been told, but a tiny, (what appears to be glass) peephole, and with a wire cage around it. (Notice we are talking, all this fuss, about 1 door, in over 300 murder camps across Europe...)

Two; no one "told me they were all gassed." Nor is that the claim. Gassing, burning, starvation, exposure, overworking, experiments, shooting, beating, etc. was the reality.

You can spend your time on 1 apparent data-point, or even 10, while ignoring the other millions, like with the lie you've been told about a door and window. Meanwhile, here is just some of the proof from the US Navy Dept. If you want...

May the victims of the Nazis be elevated, and their memory help us to forever build a better, more equitable, and peaceful world...