Machine :
MacBook Pro M1Pro 10/16cores 32GB RAM
MacOS Sonoma 14.3

Version :
Prism launcher 8.2
Minecraft 1.20.4
Fabric 0.15.7

Mods :
(DistantHorizons-fabric-2.0.2-a-dev-1.20.4.jar) - Unrelated to DH as the issue persists when deactivating the mod
fabric-api-0.91.1+1.20.3.jar
indium-1.0.30+mc1.20.4.jar
iris-1.7.0-snapshot+mc1.20.4-5983468.jar
sodium-fabric-0.5.8+mc1.20.4.jar

Error log:

composite2: composite2: WARNING: Could not find vertex shader attribute 'at_tangent' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_midTexCoord' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'UV0' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'iris_Entity' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'at_midBlock' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_Entity' to match BindAttributeLocation request.
WARNING: Output of vertex shader 'iris_FogFragCoord' not read by fragment shader
WARNING: Output of vertex shader 'zMults' not read by fragment shader
ERROR: Implementation limit of 16 active fragment shader samplers (e.g., maximum number of supported image units) exceeded, fragment shader uses 17 samplers

known issue. you're out of luck.
you'll just have to wait for me to efficiently handle my texture read/writing... which will not be any time soon

Gotcha no worries we had already warned me in the discord. Wasn't sure if it was documented yet si I figured I'll just get you as many details as possible here. Good luck and thanks for your work!

Same issue here on iMac with M3 chip and macOS Sonoma 14.4. Here is the error log:

composite2: composite2: WARNING: Could not find vertex shader attribute 'at_tangent' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_midTexCoord' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'UV0' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'iris_Entity' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'at_midBlock' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_Entity' to match BindAttributeLocation request.
WARNING: Output of vertex shader 'iris_FogFragCoord' not read by fragment shader
WARNING: Output of vertex shader 'zMults' not read by fragment shader
ERROR: Implementation limit of 16 active fragment shader samplers (e.g., maximum number of supported image units) exceeded, fragment shader uses 17 samplers

Same problem on a M1 Max Macbook pro ...

composite2: composite2: WARNING: Could not find vertex shader attribute 'at_tangent' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_midTexCoord' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'UV0' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'iris_Entity' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'at_midBlock' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_Entity' to match BindAttributeLocation request.
WARNING: Output of vertex shader 'iris_FogFragCoord' not read by fragment shader
WARNING: Output of vertex shader 'zMults' not read by fragment shader
ERROR: Implementation limit of 16 active fragment shader samplers (e.g., maximum number of supported image units) exceeded, fragment shader uses 19 samplers

Sad :/ I wanted to use it with Distant Horizons

Same on M3 Max just trying to use it with DH 😭

composite2: composite2: WARNING: Could not find vertex shader attribute 'at_tangent' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_midTexCoord' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'UV0' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'iris_Entity' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'at_midBlock' to match BindAttributeLocation request.
WARNING: Could not find vertex shader attribute 'mc_Entity' to match BindAttributeLocation request.
WARNING: Output of vertex shader 'zMults' not read by fragment shader
WARNING: Output of vertex shader 'iris_FogFragCoord' not read by fragment shader
ERROR: Implementation limit of 16 active fragment shader samplers (e.g., maximum number of supported image units) exceeded, fragment shader uses 17 samplers

read this issue here