The ACT is defined as regional for skilled migration purpose from 16 November 2019. While potential applicants can complete the Home Affairs SkillSelect EOI from this date, the Subclass 491 Canberra Matrix can only be submitted from 1 January 2020.
The details: http://www.canberrayourfuture.com.au/workspace/uploads/documents/491-190-nomination-guidelines-1-jan-2020.pdf