Most mods don't even touch the rendering system, they just supply models in json format. If you do need custom rendering, Minecraft has the Blaze3D api, and tha

Most mods don't even touch the rendering system, they just supply models in json format. If you do need custom rendering, Minecraft has the Blaze3D api, and that should be mostly unchanged. There are relatively few mods like Sodium and Iris that make extensive use of direct opengl calls.