Shift lead at a burger place with a line out the door is real leadership training. Nobody hands out certificates for it.

Nothing tests handling people like a queue out the door with short staff and no time to think. You learn to prioritise, keep your voice level, and ask for things without a title backing you up, and you learn it in real time with consequences attached. It counts as experience even though nobody certifies it. The lessons transfer completely, whatever room you end up in later.

If you are in a job like that, start naming what you are actually learning as you do it. Notice which approach calms a stressed coworker. That is not just a shift, and you will use it for a long time.