Install Create Aeronautics without the dependency mess.
Use this quick setup path for Minecraft Java 1.21.1 on NeoForge. Start clean, install the required dependencies, launch once without shaders, then add extras.
Required stack
Fast sanity check
Minecraft 1.21.1 + NeoForge + Create + Sable + Create Aeronautics. Same mod versions on client and server. Test first without shaders.
If the game crashes before the title screen, remove shader and visual mods first. Then test only Create, Sable, and Create Aeronautics.
Step-by-step setup
This sequence is intentionally boring. Boring installs are good installs.
Create a fresh Minecraft 1.21.1 profile
Do not throw every performance, shader, worldgen, and QoL mod into the first profile. Get the core stack working first.
Install NeoForge for 1.21.1
Create Aeronautics currently targets NeoForge on Minecraft 1.21.1. A Fabric or old Forge profile is the wrong first path.
Add Create, Sable, and Create Aeronautics
Sable and Create are required. Put all three mods into the mods folder, or install through a launcher that resolves dependencies.
Launch once without shaders
Shader and rendering mods can create confusing visual bugs. Make the base mod load first, then add visual mods later.
For servers, mirror the same stack
Create Aeronautics is required on both client and server. Keep versions aligned, then test with a new world before migrating an old one.
Missing Sable
Install Sable. It is not optional for Create Aeronautics gameplay.
Wrong loader
Check that your profile is NeoForge for 1.21.1, not Fabric or a mismatched loader version.
Shaders first
Test without Iris or shader packs, then reintroduce visual mods one by one.