Coffee roast temperatures are about 350 degrees.

do you worry about getting cancer from bread? Bread ovens are about 200F hotter.

Coffee roaster here, at 350F the beans have turned yellow and barely started browning. 390F~ is around the point where most roasters would consider development of flavor to really take off (yeah yeah pre-development phase, I'm keeping it short) and beans will be done at various points after that depending on roast preference.

The smoke that the roaster produces towards the end of roast is no joke, and some has to get on the beans, but I'd say it is minimal enough to not be an issue as there should be plenty of air flowing through the roaster at that point.

If roasted improperly oils could seep out of the beans while in the roaster which burn as well and stick to the beans. I'd say that is more of an issue than the smoke or roasting too dark.

350f sounds too low to me. First crack (beginning of a very light roast) is around 200c/392f. Most coffee is roasted quite a bit darker than that - e.g. 220c and above

https://en.wikipedia.org/wiki/Coffee_roasting

but the coffee turns very dark in some roast and it generates a lot of smokes during the process.

The smoke comes from the chaff of the bean and steam as the beans release moisture. The actual bean never gets hot enough to produce smoke. Unless you over roast, but then your coffee is undrinkable.

Unless you're screwing something up, coffee beans shouldn't be "burnt". I can usually taste a lot of burnt flavor from cheaper dark roasts, but a medium roast rarely seems burnt to me.

I've heard Starbucks and other big chains "burn" their beans to guarantee consistency (few of their customers, if any, are drinking it for coffee flavour).

But -- any truth to this legend?

Have you compared a raw bean to a roasted one?

They’re definitely burned!

Conflicting reports if ya search online.

If you were to concentrate and inhale the smoke from roasting beans, that would most certainly have deleterious health effects.

It stands to reason, then, that at least some of those nasties are left in the beans when they cool.

However, whether drinking some coffee is always bad will depend if the linear no threshold hypothesis is true for roasted coffee beans?

Yes. https://pubmed.ncbi.nlm.nih.gov/24325083/