Topic on Talk:Psychonauts 2
Direct3D 11 is actually supported by the game and used automatically if Direct3D 12 is not available (e.g. on Windows 7/8/8.1 or older graphics cards). It is even suggested by a developer to use -DX11 to avoid an error message (https://steamcommunity.com/app/607080/discussions/0/3047235828268020789/#c3047235828272106747).
DX11 support is definitely official, since the game officially supports Windows 7 and does not include d3d12on7.
I have been playing in DX11 mode up to the first point of no return so far with no issues nor stuttering (on NVIDIA).
(Vulkan is also supported by the engine, but the game complains about missing shaders if forced with -vulkan.)