Just spent some time over the phone with Revenu Quebec /IT support. In years past, form TP -59 required you to have a TP-64-3, but for tax year 2020, form TP-59.S clearly states it (TP64.3) is NOT required for the fixed rate method (section 2).
They realize there is a problem maybe and will have to get back to me within 3-4 business days.
I will follow up here after RQ gets back to me.
