I'm a UK citizen and am about to move to the EU (Austria, specifically). Since the Brexit transition period lasts until the end of the 2020, I can travel without a visa for now, and my current understanding is that I can stay in the EU after Brexit without applying for a visa, the same as if I had moved a year ago (source).
However, suppose that I travel back to the UK for a few days, via a different Schengen area country (e.g. France/Belgium/Netherlands), either during/after the ending of the transition period. Will my Austrian "e-card" and residency permit be sufficient to re-enter the other Schengen country from the UK, or as a non-EU-citizen, must I apply for a visa to do this?