How many branches are supposed to be created from each quantum event?

With the Copenhagen interpretation, this is cake. There’s only one. With the many-worlds interpretation, this is not so easy for my physics-ignorant mind to untangle, because many of these quantum choices don’t split fifty-fifty. You can’t have a 90% quantum chance split two ways, else we’d have experimental results giving us perfectly balanced coin tosses instead of the heavily weighted experimental outcomes. In order to get the many-world split to work at 90% odds consistently over many observations, you have to split it by some multiple of ten. Only if we imagine that ten/twenty/one hundred new branches are created can we assign the low probability outcome correctly to one of every ten. (In reality, these odds follow the Born rule and not my arbitrary choice of 90%, but you get the drift. It’s still not a coin flip.)

I’ve seen advocates of many-worlds argue that the math of decoherence is simpler than that of wavefunction collapse, and that therefore we should believe many-world decoherence instead. I’m not in a position to understand what they’re talking about, but if their simple math can’t answer my genuinely simple question about how many branches split off with the apparent collapse – all the while preserving the observed odds – then I’m not sure why I should believe them about this.

“Infinite branches” is an easy answer, I guess. Is there a finite answer about how many new branches are created every time we zing a photon off an electron? Bonus question: Is this an answer I’d be able to understand?