Each major version of DirectX is its own API, they aren't upgrades. That's why you need DX9 to run DX9 games, DX10 to run DX10 games, DX11 for DX11 games, etc. even if you already have DX12 installed.
Each major version of DirectX is its own API, they aren't upgrades. That's why you need DX9 to run DX9 games, DX10 to run DX10 games, DX11 for DX11 games, etc. even if you already have DX12 installed.