This doesn’t seem very related to iPlug2 TBH better put stuff like this on stackoverflow. probably your static library does not have arm64 architecture, only intel
This Script builds OpenSSL, nghttp2 and cURL/libcurl for MacOS (x86_64, arm64), Mac Catalyst (x86_64, arm64), iOS (armv7, armv7s, arm64 and arm64e), iOS Simulator (x86_64, arm64), tvOS (arm64) and tvOS Simulator (x86_64). It includes patching for tvOS to not use fork() and adds HTTP2 support via nghttp2.
The same project (Intel OK, Apple Silicon - lib not found ).