Most of us didn't start out being leftists. Lots of us have lib or chud backgrounds but was radicalised by material circumstances and leftist propaganda.
We want more people to turn left and we cannot do anything to change the material conditions of capitalism. We can however work to improve our propaganda so it will have a broader appeal.
To get a discussion going about what is good propaganda we could use our own radicalisation stories as a starting point.
I have always been a weird nerd so for me it was listening to long lectures on YouTube that helped move me from being a succdem to believing that capitalism has to be abolished. Around the time of the financial crash in 2008 Richard Wolff's Capitalism Hits The Fan as well as David Harvey's lectures on Marx was hugely influential in pointing out how capitalism is foundationally incompatible with human progress. Talks by Chomsky helped me realising how thoroughly evil US imperialismnwas and Parenti's content made me question the Cold War propaganda about the USSR and its allies that we are indoctrinated to see as common sense and get a much more nuanced view on things.
I got "Radicalized" by reading and informing myself, i don't think propaganda worked at all. Not even listening to the podcast did anything for me. Initially i tuned into the chapos, because of the reading series and i liked hearing them dunking on people i hate. But in general i think Felix Guattari, Mark fisher, Franco "Bifo" Berardi, Chomsky and Naomi Klein did a better job at radicalizing me than anything else.
In this sense i think that explaining people how the world works and giving them alternatives is a better way of bringing them left than any propaganda.
propaganda can be educating