I’d go with XFce. I have it installed on many old laptops that I have given away to my cousins, nieces, and mom. Works like old Windows if you modify the panels (remove the bottom dock, bring the main panel down), and then you put some sane defaults, like setting up sleep (NOTE: you will need to edit a file to make xfce go to sleep unattended), enabling natural scrolling, enabling the login manager to show username so they don’t have to type it every time, etc etc). But after all that is setup once, xfce is the best case for an old laptop.