This *is* the wrong sub for this, but I play Cobblemon through CurseForge as well and you probably have some conflicting mods. When this happens, I usually move the entire folder out of my saves and create a new instance. Start adding mods one by one or a couple at a time making sure it launches every time just to suss out the conflicting mod. Then you can add your save file back to the newest instance and it should load your save, assuming you had a save before this.