You have to know what to discuss and which holy grail to avoid.

Reddit is overwhelmingly populated by left-wing teenagers and college students -- so politics or economics discussions are shallow and fruitless.

HN is overwhelmingly populated by techies, heavily biased towards FAAMG and bay area, heavily biased towards web dev. Economics discussion here seems to be saner though with a massive US-centrism and anti-tax skew as people are 1%ers and many never experienced life outside the US, but if you dare criticise the big 5 companies or their products, prepare to be buried...

Reddit at least has lots of normal people with a decent amount of life experience.