I was a non resident of Canada in 2021. I didn't have any income.
Can you please provide more information about your problem? What is the exact error message that you are getting?
If you are getting an error while trying to NETFILE, it's because non-residents can't us NETFILE. You can mail or fax your return. This CRA page has info on where you can send your return: https://www.canada.ca/en/revenue-agency/corporate/contact-information/where-mail-your-paper-t1-return.html#nonres