Most importantly you’ll have to generate the certificate/identity for codesign to use.
Unfortunately Monterey does not give me the same symbology in the crash reports as Big Sur is giving you. Also note that homebrew M1 binaries poured from bottles come codesigned. Codesigning the app yourself will override those signature components. If you brew install --build-from-source everything, there shouldn’t be artifact signatures. They throw warnings but won’t error.
Seems like your macosx_bundle.sh may not be calculating the path for the correct gtk+3 thingies. Those errors should not be. Most other warnings in the script is ignorable and due to a bit of redundant recursion which provides for the configuration of the chain of dependencies within the set of libraries.