Question about separation of air traffic on approach

[Nicholas49]

Hello

We know that a common reason for a go-around is that the aircraft landing ahead has not yet vacated the runway. Can I ask a few questions about the specifics of this procedure?

At what stage of the approach must you go-around due to the previous landing aircraft still being on the runway? Is it when you reach a certain altitude? Does it vary from one approach/airport to another?

Is the weather a factor? Would the separation be increased in fog, for example?

Whose call is it? The tower controller or the captain? (I appreciate both can instigate a go-around.)

And if I may add a cheeky sub-question (perhaps related?): when does a missed approach become a go-around? Again, is it a certain stage of the approach?

Thanks