Yup. The very first thing in my step-by-step tutorial for
Doing a Completely Clean Reinstall of Windows 10, is this:
Important Reminder 1:
If your computer has ever had a valid, licensed copy of Windows 10 installed, even if that's been later replaced by, say, Linux, you can still do a completely clean install of Windows 10
without having to acquire a new license. Windows 10 licenses are stored electronically on Microsoft servers, and are linked to your computer's motherboard. The installer will locate that existing license if you are reinstalling Windows 10.
---------------------------------------------------
There were lots of people who didn't want to go to Windows 10 back in the early days and that took Microsoft's statements about the free upgrade period ending in July 2016 who intentionally did an upgrade to get a license linked to their machine on the Microsoft servers, and then immediately either used the rollback feature or a full system image backup to take their machine back to Windows 7 for ongoing use.
If a given machine has ever once had an activated copy of Windows 10 on it you can install whatever other OSes you might like over time on that hardware and come back to Windows 10 whenever you like, and never be asked for a product key.