Microsoft has developed a subset of DX12 for Windows 7 holdouts. This actually undermines efforts to get users to switch to Windows 10.
Blizzard added DirectX 12 support for their award-winning World of Warcraft game on Windows 10 in late 2018.
DX12 is built on WDDM 2.0 which is the baseline for Windows 10 with some incremental changes with subsequent semi-annual releases.
Windows 10 version 1809 is the current release and with a clean install it runs fairly well. We have not seen issues with old machines or new ones.