I'm under the impression that it's anybody's guess as to the cause of A-fib, and it may vary with each person. My cardiologist tells me my heart arrhythmias ( including the A-fib) are likely from scarring in the atrium ( upper part of the heart) over time caused by long term poorly controlled high blood pressure ( my bad, not wise to ignore high blood pressure) and that may be a common cause. It tends to happen as we get older. Fortunately it seems to be well controlled in my case.
My fingers are crossed for you that you will get to move into that new apartment soon and the move will go without a hitch. And of course, that you and your birds will be happy there. And a Happy New Year to all of you as well. May 2024 not be as wierd as any number of us think it may be.