Some NTT versions have shader_create and alike - do /gmlapi in chat to get a full list of functions.
I am currently working on a new NTT update (if you own regular Nuclear Throne on Steam, you can find an early preview version on “ntt_development” beta branch) but I cannot actually guarantee that custom shaders will continue to be supported since they first relied on an extension (“Graphics Utilities”) that no longer works in GMS2 and then on an extremely hacky solution by me (that doesn’t work with current versions of GMS2).