It's, it's the very definition of immeasurable and theoretically anyone featuring that could be immeasurable, the problem is the amount of variable that creates a situation where the character isn't immeasurable.
For example, when characters time travel using FTL speeds under specific situations they technically are going "beyond the limits of time and space" under a relativist framework but is a limited experience that isn't natural to their own existence and can only be done for that specific thing in that specific moment. Before some characters got "immeasurable while time traveling", but I think that has been removed as just adding Time Travel by the speed in the abilities would give the same thing and not imply that they somehow were "much faster by nature".
The same to things like machines that under a very specific moment can time travel or access a higher dimensional plane where they can move freely across time. A lot of the time anyone can experience those realms and use them to travel across space-time without the need for some kind of superior existence. That is, the nature of the realm is immeasurable, but it allows the ones inside of it to do immeasurable feats without being immeasurable themselves, I think that is a good explanation.
In cases where that doesn't happen and, for example, the realm is impossible to be understood by anyone that doesn't share the nature of the realm, then in order to move across that realm you would need to also be transcendental yourself and that would fit immeasurable (Unless, again, it has a specific ability that allows for movement across that realm).
In theory, transcending linear time is by definition immeasurable, but in fiction, there are a lot of moments when that is done without fitting the idea of someone being naturally immeasurable and is instead taking advantage of some specific cosmology rule or special ability, so they aren't "naturally above space and time". So the immeasurable speed is given on a case-by-case if the characters themselves are transcendental to time and space and there are no loopholes that just make everyone share immeasurable even when they logically shouldn't, then immeasurable is a fair game.
I don't get where you said that immeasurable isn't "being beyond time" when the Speed page directly states that it's "movement beyond linear time" and it explains why it's case-by-case and gives examples of why they do that. The right way of saying would be "Immeasurable is movement beyond linear time, but given specific conditions that are fairly common in fiction, it's better addressed as a case-by-case situation in order to verify if it's something in nature for the character and not a one-off ability".
