From January 1st 2021 until December 31, 2021, all Brits living in Austria will need to apply for the Article 50 card to exercise their right to remain and work in Austria under the withdrawal aggreement. Graz is already taking appointments, but as you have a whole year to apply there is no rush!
Documentation: You MUST have a Meldezettel dated before Dec 31st 2020 in order to be eligible. If you have been here longer than 4 months, you should also have an Anmeldebescheinigung (unless you arrived before 2006). If you don’t have one yet, it won’t stop you getting the Article 50 card, but you can expect a fine. If you have been in Austria for longer than 5 years, then having the Bescheinigung des Daueraufenthalts will get you a 10 year residency card (instead of the 5 year one) and will cost you less too. More detailed information on how to apply for the Article 50 card can be found here (including documentation, income requirements etc).

The admins in the FB groups below have also created an excellent website with lots of information for Brexit and other issues – British in Austria Network .
For more information on Brexit, questions about our rights under the withdrawal aggreement etc, this is a very useful facebook book – British in Europe – Austria (they are part of the British in Europe coalition group which work together to represent the thousands of Brits living and working across the continent).
For general questions for Brits living in Austria – this is another very helpful group – British in Austria
I would recommend reading up on what is allowed under the withdrawal aggreement – for example with the 5 year residency card it’s only allowed to be away from Austria for up to 6 months a year (exceptions can be made for studying, pregnancy etc), otherwise you lose your right to remain. For those with the 10 residency card, it’s allowed to be away from Austria for up to 5 years.