Bitmap ResourcePack Won't Load On Vanilla

[buoyant bone]

I've tried every angle seemingly. But ever since updating to 1.21.5 from 1.21.1 these resource packs' break the entire resourcepack so it won't load on vanilla clients! But it loads perfectly fine for modded clients like Optifine.

[charred flicker]

Did you check with the rp author if they even support that mc version

[buoyant bone]

I am the author

I'm struggling to get it to update. I have been copying ways the other functioning RP on my server. Because I have over a dozen unicode bitmaps that work, but whenever I try to replicate that with the layout of this RP it breaks the whole thing