The problem is that, if alternate universes are springing off for every possible outcome of every event anywhere, that signature must be constantly changing as our POV incarnation of the crew weave through the possibilities?
The quantum signature of the Trek universe we observe with our heroes however would likely not change.
The only situation for Trek I could see the quantum signature of the 'prime universe' changing is significant alteration to the timeline. Which begs the question, what happens to the original frequency/signature?
It is likely altered, or temporarily super-imposed with another one, and most of the time we see temporal 'incursions' which end up being fixed... bringing the universe in sync.
Other times, we could be seeing a 'merger' of the two... in which case, the original universe/frequency would alter during the merger, but ultimately stabilize into its original frequency (literally 'eating up' the other one while integrating it into itself).
It is also possible that some predestination paradoxes we observed in Trek would likely be necessary. An occasional alternate reality intersects by manifesting itself as a timeline disruption, prompting our heroes (from the original timeline with memories intact, or coming by info that changes were recent and need changing) to use that information and set things right.
Keep in mind that the multiverse theory theorizes there are infinite number of universes, as such, there might not be new universes forming at all, just infinite universes interacting with each other in certain ways as can be seen in this study:
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013
So... why would new universes need to be created if you already have an infinite number of them interacting with each other?
It's all energy and motion... and if you want to simplify it even further, in some cases, we might even see a 'broken telephone' playing out with universes interacting with each other... namely, the farther apart universes are, the interaction might end up going through changes, interruptions even, and some data loss may occur, resulting in greater and greater changes the further apart you move away from the universe in which you originated.
Granted, my understanding of the subject is relatively limited, so this might not happen at all.
There's also something else to consider.
I remember reading (admittedly on Wikipedia) some time ago that there's a difference between what we call an 'alternate universe' and 'parallel universe'.
Namely, in an alternate universe, only certain events will differ (such as people's choices, evolution of Earth, the existence or Earth, and so forth) while in parallel universes the laws of physics would differ.