It confirms the issue is related to pip not installing PyCryptodome binaries for the ARM architecture. I can’t do anything about it, since it’s a PyCryptodome issue that seems to have already been reported.
In any case, the workflow will only prompt you to install PyCryptodome if you try to decrypt a PDF file encrypted with AES or RC4 standards.
I'm still curious to know what @giovanni did to get it to work on his ARM Mac.