What’s the alternative aside from forced sterilization and starvation to decrease the human footprint?

Human land use is incredibly inefficient. As a simple example, in the US the vast majority of corn production is ethanol or animal feed (which is incredibly inneficient on a calorie basis). Then when you take into account low density residential and their endless lawns (turf grass has by far the most acres of any crop in the US) and a million other poor uses of land and there's a lot we can do, even at 8 billion people, without destroying every forest.

The issue isn't that the problem isn't solvable, there are tons of things that have huge environmental benefits. The problem is that these generally require some sacrifice (e.g. denser housing with much smaller lawns, eating more resource efficient foods like lentils, moving away from fossil fuels) but there's not sufficient collective will for actually doing these things.

Pretty sure there’s a middle ground between “forced sterilisation” and “boil humans to death in 50°C heat,” don’t you?

Hint: The birth rate of a population is inversely correlated with wealth.

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

Educate women? Isn’t that broadly considered to reduce birth rate?

Cutoff petroleum-derived fertilizer except for those who can afford carbon credits.