Why You Can't Find Environmental Materials Items in JEI or the Creative Menu
If you have Environmental Materials installed and cannot find any of its items in JEI, REI, or the creative inventory, this is expected. The mod registers zero items and zero blocks.
Checking Your Installation
Before assuming something is broken, verify the mod is actually loaded. Open the mods list from the main menu and confirm Environmental Materials appears there. If it does not, the mod is not installed correctly and no amount of searching in JEI will help.
What to Search For Instead
Because the registry is empty, there are no item names to search. Do not look for blocks with "environmental" in the name, and do not expect new ore, wood, or stone variants. Any search in JEI will return nothing from this mod.
If You Expected Content
If you installed Environmental Materials expecting new building blocks or materials, the current build does not provide them. The mod's registry contains no entries, so there is nothing to obtain, craft, or place. Remove the mod if you need the slot for something else, or keep it if another mod or config depends on it being present. Either way, do not spend time hunting for items that are not there.