It’s usefulness is in it’s simplicity, not in the accuracy or precision at an individual level.

Especially if you like lifting weights you can get some wild errors.

Is your definition of socialism basic needs met or something else?

The Nordic countries gets close to the food, shelter, medical being met. Homelessness (sleeping in public) was surveyed at 0.04% according to first Google result (Sweden 2023). Healthcare is not free but very cheap.

Anyway if that qualifies then yes, birthrate is less than replacement level.

French is probably the most wide spread. Mandarin has most people, but only in one country.

How far away do you want to build your new mountain?

You could flatten it, take the top of and put on the sides, but if it’s bad quality stone that may just not be possible.

I have to walk the dog, so I get myself out. Once I’ve started walking doing a little longer than the bare minimum is not too bad. If the weather is nice it’s actually quite enjoyable.