The prompt works for me and correctly identifies that zstd doesn't work https://chatgpt.com/share/689769c5-bd68-800b-ae63-c6a337dcfa...

"Short answer: you can’t. iOS doesn’t ship a Zstandard (zstd) encoder/decoder in any first-party framework. Apple’s built-in Compression framework supports LZFSE, LZ4, zlib/deflate, and LZMA—not zstd."