Found it here https://www.canada.ca/en/revenue-agency/services/tax/international-non-residents/individuals-leaving-entering-canada-non-residents/non-residents-canada.html in the Which income tax package should you use? section, right above the Filing due date heading.
"Due to international mail delays, the CRA is temporarily accepting non-resident income tax returns through fax. You can fax your return to the tax centre applicable to your country of residence."
I haven't done my taxes yet. If you successfully send yours by fax please let me know. Thanks very much for posting this.