Using ETF 7.0.13 with Fabric
A resourcepack structured like this:
assets/minecraft/optifine/random/entity/
creeper/creeper2.png
chest/normal2.png
pack.mcmeta
makes creepers have random textures, but all chests remain the same. The resourcepack works properly in 1.21.8 and below.
This issue occurs with OptiFine in 1.21.11 but I have not tested previous versions.
1.21.8:

1.21.9:

Using ETF 7.0.13 with Fabric
A resourcepack structured like this:
makes creepers have random textures, but all chests remain the same. The resourcepack works properly in 1.21.8 and below.
This issue occurs with OptiFine in 1.21.11 but I have not tested previous versions.
1.21.8:

1.21.9:
