I have the same problem. It has been closed as a duplicate issue, but I hope you will find it helpful as I describe what I know about this problem.
https://bugs.mojang.com/browse/REALMS-11454
Oddly enough, the same problem occurs when I press the sign-in button and wait a few minutes at the screen where the QR code to log in appears. I am not signed in at this time.
devdazy
REALMS-11454
I have the same problem. It has been closed as a duplicate issue, but I hope you will find it helpful as I describe what I know about this problem.
https://bugs.mojang.com/browse/REALMS-11454
Oddly enough, the same problem occurs when I press the sign-in button and wait a few minutes at the screen where the QR code to log in appears. I am not signed in at this time.