Many worlds is just the claim that the Schrödinger equation holds in actuality.
I don't think QD makes decisions 'uniquely'. Take this quote,
> The step from the epistemic (“I have evidence of |π17〉”.) to ontic (“The system is in the state |π17〉”.) is then an extrapolation justified by the nature of ρSℰ: Observers who detected evidence consistent with |π17〉 will continue to detect data consistent with |π17〉 when they intercept additional fragments of ℰ. So, while the other branches may be in principle present, observers will perceive only data consistent with the branch to which they got attached by the very first measurement. Other observers that have independently “looked at” S will agree.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9689795/
Emphasis on "the other branches may be in principle present" — the claim at least in this paper can't be that all branches agree, just that they agree locally.