For a really low end computer, that is typical. Go to Windows Update, manually install everything, let it finish rebooting multiple times through the rollups and service packs and major releases. The symptom is probably because of slow eMMC storage, Windows Update behaved simlarly in the days of mechanical hard drives.
No business will buy that, anyone spending that much on hardware will want a warranty.
Those Elitebooks have a bottom that slides off with a single latch, with an easily removable battery, that’s the first thing you should have done.
You successfully did the factory reset, they will be ready to type in their MS account. I would recommend following these steps to bypass the MS account and making a local account account for the future customer, just so there is no reason to return it to you.
https://www.tomshardware.com/how-to/install-windows-11-without-microsoft-account
This is why Dell puts the plastic cover over the integrated graphics.
It will do one thing, and that is browse the internet with not too many tabs. It will play Youtube and Netflix. If you’ve followed advice in this thread and did the reset and you still hit “Enterprise Enrollment”, you could try calling up the school and asking them to deprovision it, its unlikely they want it back.