There is an interesting argument amongst smart people - so nobody who equates Keynes with neoliberalism - that Keynes is a form of neoMarxism, because both Marx and Keynes, from different starting points, and with different conclusions, reject Say's Law.

i think keynes pretty clearly strongly disagreed with marx’s political agenda (the manifesto) but was well acquainted with “capital” and thought there was value in it - but also that keynes wasn’t really wrestling much with big questions of political systems as much as practical solutions

The big difference being that for Marx the collapse of Say's Law was a contradiction of capitalism that would be overcome by revolution, while Keynes believed it could be manages by state intervention.