I mean there are a bunch of studies and articles, with an extreme wide range. It also difficult to count. For instance if a heat wave leads to heart attack in an obese person, should that be included, etc.

UN org claims 3.4 million per year by the end of the century: https://www.v-20.org/new-health-data-shows-unabated-climate-...

See other one here: https://www.forbes.com/sites/dishashetty/2021/07/30/climate-...

In general it's very rough, many things are hard to predict