Not to discourage further discussion, as there is always more to be said, but you may be interested in this previous questions When did Americans, and the rest of the world, discover the atrocities towards Jewish folk during World War 2? Was it known about prior to our entry to the war, or only discovered after reaching Germany and happening upon it during the campaign? (by u/commiespaceinvader).

Although the linked discussions go into far more detail than I can, the TL:DR is that the Allies knew about the Holocaust has it was occuring. Intelligence reports (for example The Einsatzgruppen Situational Reports USSR), were intercepted and decoded which detailed the killings very clearly. Furthermore, spies from the Armia Krajowa (The Polish Resistance), broke into Auschwitz and smuggled out reports of the camps operation, trying to raise awareness in both the UK and the USA. This information led to a formal commendation by the Allies in December 1942. Despite access to this information, little was done by the Allies to prevent the killings.