I was not aware that the KPD had ever cooperated with the Nazis. I’ll have to read up on that.

In August 1931, to capitalise on their growing popularity, the Nazi Party launched a referendum to overthrow the Social Democratic government of Prussia. At first the KPD correctly attacked it. Then, three weeks before the vote, under orders from Stalin's Comintern, they joined forces with the fascists to bring down the main enemy, the Social Democrats. They changed the name of the plebiscite to a 'Red Referendum' and referred to the fascists and the members of the SA as 'working people's comrades'!

Fortunately, the referendum failed to get a majority. With the recent electoral successes of the Nazis, such a referendum victory would have brought Hitler to power two years earlier.

The lunatic actions of the German Stalinists failed - but they learnt nothing. 'Today the Social Democrats are the most active factor in creating fascism in Germany,' declared Thaelmann. It was a mad adventure that served to disorientate the proletariat and facilitate the success of the fascists.

https://www.marxist.com/germany-sewell-chapter-7.htm

Still, I think it’s a bit far-fetched to see the KPD as Hitler’s enabler. After all, the Communists were one of the Nazis’ main enemies and put up considerable resistance until the end (as did the SPD, which exists again today as a (somewhat) social democratic party under the same name after being banned following Hitler’s seizure of power).

It's more that they were useful idiots who preferred to step aside when fascism reared its ugly head with insane and unrealistic accelerationist hopes, or in some cases, side with the Nazis against the 'social fascists' of the SocDems in alliances of convenience.

I was not aware that the KPD had ever cooperated with the Nazis.

It was not really a collaboration, but a united opposition against the democratic parties in the parliaments.

As the communists were already excluded from the Reichstag in 1933, the SPD was the only party opposing the enabling act (Ermächtigungsgesetz). The speech of Otto Wels in 23rd March about dismissing the enabling act (Youtube, English transscript) is famous for being the last free speech in the Reichstag and often analysed at school in Germany. Its most remembered phrase "Die Freiheit und das Leben kann man uns nehmen, die Ehre nicht!", ("Freedom and life can be taken from us, but not our honor") is divinatory for the dark years that followed. According to Willy Brand (SPD, chancellor from 1969-1974), beside his manuscript Wels carried an ampoule with poison for the case the "guarding" Nazi SA men would detain him during or after his speech.