I did address Auschwitz. The four working gas chambers in Auschwitz (the buildings we say were cremas and gas chambers, and deniers say were jus cremas) were demolished on Himmler's orders prior to the arrival of the Red Army, for obvious reasons. That is why these buildings are in ruins today.
However, we have plenty of contemporaneous doucmentary evidence showing that the buildings were gas chambers. Construction records referring to one of the buildings call it a "gassing celler", German orders for air-tight doors with peepholes were placed and fitted on the buildings we say were gas chambers, We also know that the buildings were ventilated with fans, which makes no sense if they were merely morgues or cremas, as deniers claim, but makes perfect sense if they were gas chambers (the ventilation would allow the Germans to air out the gas chambers, thereby preventing off-gassing of the kapos who went in to collect the bodies).
We also have forensic evidence indicating that the ruins of the gas chambers have substantial residue of Hydrogen Cyanide.
As for holes, they cannot be seen to the naked eye, have been found in the blown up ruins of the gas chambers at Birkenau. The fact that they cannot be seen to random tourists passing by the cremas (which are basically mounds of collapsed wall and mortar) led to some boomer football spiking in the 1980s, hence the meme you refer to.
More recently, in 2004, scholars burrowed beneath the demolished ruins and found the holes -
https://academic.oup.com/hgs/article-abstract/18/1/68/648579?redirectedFrom=PDF
I could go on but if you are even remotely open minded you will recognize that there is forensic evidence of gas chambers at Auschwitz, which together with all the perpetrator testimony attesting t othe gas chambers (including in non coercive situations, out of court and in private conversations), numerous contemporaneous German documents referring to the general policy of exterminating Jews including references to gassing, and of course the problem of the disappeared millions Jews in the Nazi camp system, make for a compelling argument.
As for Majdanek, see pic related, including the Prussian blue stains in the gas chamber.