Iris Error: No More Available Texture Units While Activating Sampler

What it looks like in the log

java.lang.IllegalStateException: No more available texture units while activating sampler shadowcolor0

How to fix it

1. Open Video Settings > Shader Packs > Shader Pack Settings (or edit the matching .txt file in your shaderpacks folder) and lower the Profile from High to Low, disabling extra features like 3D clouds, custom textures, or colored shadows.
2. Switch to a shaderpack that uses fewer texture samplers, such as MakeUp - Ultra Fast, Sildur's Enhanced Default, or Complementary Shaders on Low/Potato settings.
3. If you are on macOS, keep in mind that Apple's OpenGL driver permanently caps shaders at 16 texture units, so only shaderpacks explicitly supporting macOS will load without hitting this limit.
4. If you are on a Windows or Linux PC with both integrated and dedicated graphics, configure your OS graphics settings to run Minecraft's javaw executable on your dedicated NVIDIA or AMD GPU rather than integrated graphics.

Check your own log