i'm curious, how do you write sufficient alt text for flow charts? (emphasis on "sufficient" for complex charts)

obviously you could say something like "a flow chart about a topic.." but how would i go about describing the contents? for a basic chart it might be simple but take something like the attatched image for example (or sometimes even more complex)

image stolen from stackoverflow

i'm concerned about the topic im general, but my main motive is for something to be placed on a website, this so if there's some accessible implementation in HTML that i'm not familiar of, feel free to point it out.