When loading the shader, I get an error with this information:
text_bg.vsh: text_bg.vsh: 0(108) : error C1503: undefined variable "entityId"

I'm using the dev version to make DistantHorizons work.

ive seen this error before. the file it says is erroring doesnt actually exist within the shader. if i remember right, its caused by iris's patcher being different across verisons, and i accidentally relied on it on newer versions. which means on older iris versions, this error would happen.