yes, this is true.
even the most heartless and cruel Nazi soldiers will eventually be traumatized by hearing the dying screams of women and children.

not to mention it was a huge waste of bullets and trained men that could serve on the front line. so they tried to separate the killer from the kills as much as possible.

their first attempt was to put the jews in sealed trucks, with the exhaust pipe connected into the cargo bay. so the smoke will kill everyone inside.
this did this in the Chelemeno concentration camp.
but even that idea was good enough because now the drivers became traumatized and it was a waste of fuel.

and only then the gas chambers were invented.
gas chambers only killed about 3 million jews, the rest were murdered by Nazi brutality and their supporters in eastern Europe.

anyone who thinks that "holocaust is fake cuz gas chambers could kill 6 million jews" is a moron

Or that said opinion can be dangerous in regard of the context.

It's not for nothing that negationism is a crime in a lot of European country, nobody don't want NAZI 2.0