This is such a confusing topic and also a difficult topic to research, partly, because there are so many different questions people want to have answers for.
The one the OP asks here seems to be if medical transitioning reduce suicides by transgender teens? (Is it near-future reduction we are talking about or lifetime reduction? Ideation versus completed suicides? As was pointed out on this thread earlier, women and girls have higher suicidal ideation and attempts, but men and boys complete more suicides, largely because they pick more irreversible methods)
But that, then is linked to a slightly different question, i.e., what percentage of children and teenagers who identify as transgender at some point stop identifying that way later. That group would not be helped by medical transitioning, so its size matters, and studies of measuring regret are extremely difficult to do.
Most we have are either from the era when gatekeeping was much more rigid against transitioning or use data from a source (such as gender clinics) which is likely to miss most detransitioners (who may not go back to where they transitioned). And the recent increase in teenagers transitioning may alter the rate of regret in the near future, too. Or not, but so far we don't have good studies on that, though some suggest higher regret percentages than one or two percent.
Then there are the large problems in how to find a good sampling frame (the places where individuals are contacted and asked to participate in a study, which should not be more likely to select some sub-group of people only), and good control (comparison) groups for the group we are interested in.
When a study is about the effect of medical transitioning on reducing suicides, the control group should ideally be people exactly like those who medically transition, except for that transitioning bit.
So comparing the medically transitioned to general people of the same age, sex, race etc. in the same country is not that good, given that those who transition differ in their identity, and probably in how they are treated and also often in how many mental health conditions they might have and the rates of neurodiversity and gay/Lesbian orientation.
All those other variables are linked to higher suicide rates so should be controlled for if we wish to study ONLY the effect of medical transitioning versus not.
But even trying to find people who considered transitioning and then did not would not guarantee a good control group, because the two groups differ in what they chose to do and that choice, in itself, may hide an additional unmeasured difference between them.
This is not to say that we can't get any useful information about this topic, but there will always be a debate about how to interpret it, at least until a couple of more decades have passed. Still, I would argue that we should focus on completed suicides more than on suicidal ideation in this context, given that suicidal ideation is high in many teens in general and, in particular in teen girls. (That is a separate and important problem to study, but it's separate from this one.)