Is it possible a laptop from the beginning Windows 10 down to Windows 8? (Will not do it, just out of interest)
If you have a license key for Windows 8, of course. Simply download the system, mount it on a USB stick or burn to DVD and install.
However, that would not be advisable. Even apart from the arguments between Windows 8 and 10, hardly a notebook manufacturer bothers to support different operating systems. Older than the delivered system can therefore result in missing or incorrectly working hardware drivers.
You have to reinstall windows 8 … Rollback is not possible because it is not an upgrade.
Whether the key of Windows 10 works I do not know.
I would guess that you need a new one.
"Down" in the sense of "Downgrade while retaining the data" is not possible.
A complete reinstallation might work if:
a Windows 8 product key is present
the manufacturer provides drivers for Windows 8 (which is unlikely here)
The question is very hypothetical, because zero would make sense.
