that was true of intel but definitely not of arm macbooks.

Then why do they have fans?

Many ARM Macbooks do not have fans?

Many do. I would argue most do, although i don't have air vs. Pro sales numbers so I can't speak definitively there.

Even those that don't may rely on passive cooling strategies that are less effective in enclosed spaces.

Fans !== heat

My comment is only in response to https://news.ycombinator.com/item?id=48701824 , which is contending that ARM Macbooks have fans.