I have just installed the 1.21.5 ETF version and checked if my resource pack was working, but then I discovered that if you use more than 1 color for the naming of the mob then the custom texture is not being applied:

my .properties file
skins.1=2
name.1=iregex:.(Angel).

Multicolor name:

One color name:

Its actually name.1=iregex:.(Angel). with the * symbol, I think it was written in cursive because of formatting