I'm not sure about this, if anything there seems to have been a few services recently (e.g. DuckDuckGo, Qwant) that are supported by ads (presumably with metrics on ad performance for advertisers) but without following you around the internet. They seem to be doing ok as businesses, and it seems a reasonable compromise to me.

I'm curious about how Telegram will decide what ads to show, how heavily it will try and personalize them; will the ads be relevant to the channel you are in or follow you around Telegram.

FWIW, personally, I like the idea of a choice of ads or paid subscription best.