how to make boot key for monterey

Hello everyone and sorry if I express myself not well, I am French and I translate the text.

I have a macbook of 2015, I used it with ventura thanks to open legacy patcher, I recently bought a macbook M1 and so I want to give the 2015 to my nephew, I can not put it back in original system and I think that reinstalling my bone with a usb keys will solve my problem, my M1 is under tahoe and do not seem to be able to download the old versions