Shadermods, like Iris, Oculus, Optifine, are only partially supported. Shaders only work with the fallbackrenderer active. This gets activated by default if loaded with Iris and Oculus. This can be deactivated in the Config or force activated if other mods create issues with Truly Modular's Rendering
Truly Modular uses an Automatic compat by default, this means most mods Swords and Materials should get picked up, dedicated compat is possible through datapacks.
is not planned. There are many features in Truly Modular which have a significantly higher priority than backporting. Once the list of ideas is smaller we might consider backporting.