I’d recommend either Peppermint OS or Lubuntu as lightweight distros for an old laptop. There are many more distros that you can try out there, even without desktop environments (no graphical stuff, which saves a lot of resources), if you’re not into using your laptop for stuff outside of server-use. For that, Debian is the go-to imho. Just remember not to select any desktop environment during the installation process.

Put some of the distros on a flash drive and try them out. Distro hopping can be fun :-)