If I understand the question correctly, I’d say it very much depends on whether the coin is real or hypothetical/perfect. In the latter case, I think the measure either increases by 0 or by a minuscule amount (depending on whether many worlds means infinitely many). But if it’s a real coin, it should come down to questions like ‘at what point in the process of flipping is the result determined’, which sounds like a messy (quantum) physical and biological question.
If I understand the question correctly, I’d say it very much depends on whether the coin is real or hypothetical/perfect. In the latter case, I think the measure either increases by 0 or by a minuscule amount (depending on whether many worlds means infinitely many). But if it’s a real coin, it should come down to questions like ‘at what point in the process of flipping is the result determined’, which sounds like a messy (quantum) physical and biological question.