So, could a red-brown alliance actually work?

Most post-war fascists and national socialists were of this nature, working with Latin America and Middle Eastern leaders, and even the USSR too. Look up Otto Ernst Remer, Francis Parker Yockey and Johann von Leers as prominent examples.

I don't think allying with western communists/marxists will work as like you said they're all just neoliberals with communist aesthetics because everyone knows being an unironic liberal is cringe. But non-western enemies of capitalism are all potential allies.