If your home server is enough for your needs, then you can use old laptops for thin clients (tv box, audio streaming client, arcade emulation pc, that kind of thing).

You can also divide and conquer the work of your home server, a download and file manager client, a steam-cache server, a cheap backup nas, CCTV server, home-automation stuff.

This is just a few ideas from the top of my head, but the best use I got from old working laptops were to modernize them (new battery, ssd, Linux) and gift them to people who needed them (students, elderly, etc)