I have family and friends that are trans, so I have been able to kind of follow their outcomes over the years.
Human gender identity and sexuality does seem to fluctuate somewhat, but it doesn’t seem to me to be random. Some people fully identify as one gender but like to perform as a different one. Other people don’t vary at all. In cases where people “change their mind”, it’s usually because they get discouraged about being able to successfully transition, or they experience severe harassment/workplace discrimination. Just in my anecdotal experience, it’s never because they just randomly decide they no longer want to be trans
No one is getting permanent gender affirmation treatment until they are old enough to know and have been in discussions with doctors for years. I’m sure there are exceptions where some poor 5 year olds parent(s) treated them without medical oversight but it’s not common and no one wants this.