I want to convert the id_rsa file to ppk file. I found there are many websites teaching "how to convert ppk to rsa in MAC" but not vice versa. Is there a way to convert rsa private key to ppk for windows to use from MAC?
Install PuTTY via homebrew or Mac Ports and specify the output format:
puttygen id_rsa -O private -o id_rsa.ppk
PuTTY on Windows will load the OpenSSH format key (that you have copied from macOS to Windows), but command line options will not save it non-interactively. Do so with the menu options: Conversions > Import Key; File > Save private key.