FYI if anyone is running into problems installing grpcio an M1, adding

[subprocess-environment]
env_vars = [
  'GRPC_PYTHON_BUILD_SYSTEM_OPENSSL=1',
  'GRPC_PYTHON_BUILD_SYSTEM_ZLIB=1',
  'GRPC_BUILD_WITH_BORING_SSL_ASM=',
]

worked for most of my coworkers except 1. For them, we found adding the additional env vars

export LDFLAGS="-L/opt/homebrew/opt/openssl@3/lib"
export CPPFLAGS="-I/opt/homebrew/opt/openssl@3/include"

did the trick. (Assuming you use

brew install openssl

)