Even if you are considering applying to take Austrian citizenship, it would be advisable to apply for the Art 50 EUVAufenthaltstitel "Artikel 50 EUV" The Aufenthaltstitel "Art 50 EUV" is a residency title to be issued to British citizens from the end of the transition period. Its name is derived from Article 50 of the Treaty on European Union. The "Titel" refers to the document or card itself, and not the right, or permission that it confirms. card in 2021 to cover the eventuality of your naturalisation procedure taking a long time (even the swiftest procedures take months as a minimum).
Naturalisation may require you to prove proficiency in German language and display an adequate degree of integration, whereas the Art 50 EUV card does not stipulate having attained a certain language proficiency.
Austria does not typically allow dual citizenship, so naturalisation apart from under a couple of very specific circumstances would require you to renounce your British citizenship.
One blog – From Brexit to Ex-Brit – covers the naturalisation process in detail.
It should however be noted that from after the end of the transition periodTransition Period The transition period (also referred to as the implementation period) is the period following the UK's departure from the European Union (on 31.01.2020) until the end of 2020. An option to extend this period has not been taken up by the UK government., British citizens naturalising can expect to be treated as third country nationals (this will remove some of the pathways for naturalisation that are only afforded to citizens of other EU Member States.)