Deleting saved content in a past use MBA
I upgraded from a 2017 MBA running Monterey 12.1 to a new M1 MacMini, running OS12.1 Almost all files on MBA are duplicated on the MacMini. I wish to erase all the MBA's content (except Monterey, in order to sell it), without disturbing or losing all content in the MacMini. I use iCloud as opposed to an external HDD. How do I go about this to achieve my objective ?
MacBook Air 13″, macOS 12.0