Well, not doing it on your own time is the exact point of the article linked. I mean, if you want to pivot into a completely different career in a completely different company you should do it on your own, sure, but GP wants to change position within the same company, and wants to move in an understaffed department. Why should they do it on their time and dime?
Well maybe talk to the backend lead at the same time. His own team lead <> the company and the company might not even realize it. From the pov of his own team lead, it might be a purely damaging move (has to find alternative, has to explain to upper management, etc.).
TBH I wouldn't expect any manager (especially it's just a lead, not even a mgr) to sacrifice for my own benefit. I thank them and provide material reward if they do, but I'm 100% with them (and study on my own, then leave the company) if they don't. It has to be mutually beneficial, or at least looks like. So my feeling is that both OP and his team leader are not good at communication.
