ArcheryAce
Comments
I want to add in a Comment here as I have found the issue.
Yes, This IS a Minecraft bug.
I went further into this and Decompiled both 1.21.3 and 1.21.1 jar file versions to find that 1.21.3 is missing these two shader program files. rendertype_armor_cutout_no_cull.vsh (Vertex shader program) and rendertype_armor_cutout_no_cull.fsh (Fragment Shader).
Which that log you have gotten is complaining that Minecraft can't find the VERTEX version of the shader program (rendertype_armor_cutout_no_cull.vsh). Of course it will not be able to find it since in the 1.21.3 version of Minecraft. The files which hold those programs do not exist.
Currently, the only fix is to run on 1.21.1 sadly as that version has the required shader program.
Hope this helps someone as I have been struggling with it for a while.
I just did the work for you. I told you exactly what the problem was.
Yes it happens in vanilla, and I do not have a resource pack that I am able to share that will cause this issue.
I said the steps on how to reproduce it. are you able to not do that? Im sure you would probably know more than I do on what will trigger the use of rendertype_armor_cutout_no_cull.
And please do not mark this as Resolved. There was nothing done here.