Thanks to Stefano Mtangoo's comment and answer, I fixed this by manually add cmake arguments to the fomula file.

1. Install the dependencies of libzip from homebrew.

brew install zlib bzip2

2. Add homebrew libraries to CMake definitions.

brew edit libzip.rb

change L22 from

    system "cmake", ".", *std_cmake_args

to

    system "cmake", ".", *std_cmake_args, "-DZLIB_LIBRARY_RELEASE=/usr/local/homebrew/opt/zlib/lib/libz.dylib","-DBZIP2_LIBRARY_RELEASE=/usr/local/homebrew/opt/bzip2/lib/libbz2.a", "(... rest of the args.."

(/usr/local/homebrew is my homebrew prefix.)

3. Reinstall libzip.

brew reinstall --verbose libzip

notes:

You can use brew reinstall --verbose libzip --interactive to prevent the deletion of working directory and inspect the source.

Then use grep to find the broken cmake definitions and rerun *cmake ... * to test the settings.

I have tried set PATH/LD_LIBRARY_PATH, but it not works.

Good summary. I did not need 2 and 3.

Then for the signature

11. You need to start XCode and add an account.

Add an account to XCode

Download a certificate

12. In terminal check with certtool y for your new Signing Key. It's named like:

Common Name     : Apple Development:
[email protected] (xxxxxxxx)

Still with your user in the terminal sign the file (move it back if not anymore in the build folder, otherwise you end with a permission error)

codesign -f -s "Apple Development: [email protected]" /usr/local/lib/php/extensions/zip.so

Move it to the target folder, run php --version and you end with:

PHP Warning: PHP Startup: Unable to load dynamic library 'zip' (tried: /usr/local/lib/php/extensions/zip (dlopen(/usr/local/lib/php/extensions/zip, 0x0009): dlopen(): file not found: /usr/local/lib/php/extensions/zip), /usr/local/lib/php/extensions/zip.so (dlopen(/usr/local/lib/php/extensions/zip.so, 0x0009): code signature in (/usr/local/lib/php/extensions/zip.so) not valid for use in process: mapping process is a platform binary, but mapped file is not)) in Unknown on line 0 PHP 7.3.11 (cli) (built: Feb 29 2020 02:50:36) ( NTS )

Ok, i looked around the internet (insightful resurce), and the bits i found paint a dark image. In short: It's not possible anymore with Mac Os Catalina.

The errormessage tells it too. The Php environment is signed as system component (platform binary) and is installed by default. Mac Os Catalina enforces that platform binaries only load code which is also a platform binary. Which one can not do, because you are not Apple.

Leaving two possible options. Disabling the whole Signature enforcement stystemwide whic is a bad idea. Or setup a replacement Php completely selfbuild or with homebrew.