What is the most effective way to save the photos and videos and maybe also a few texts from 4 old (partly really old and long unused) laptops?
Plug in the hard drive and drag and drop the images onto the hard drive
Buy a large USB stick and copy whatever is of value onto it.
Always double, external hard drives, USB or cloud storage
Just read a little and understand: https://www.test.de/Backup-So-sichern-Sie-Fotos-Videos-und-Dokumente-1365545-0/
Videos can reach a size that a USB stick is not as efficient as an external drive. Ideally a USB HDD with at least 1 TB, that should be a long time.