I went to the additional security options page (https://account.live.com/proofs/manage/additional) (was able to sign in to this fine by getting a code sent to my son's email) and on this page selected the Change Password option.
I don't remember previously having set a password for this account so it's possible it was set up as passwordless. Now when I sign in at https://accounts.microsoft.com I use a password (the first time after changing the password I had to select the option on the sign in page to use a password rather than sending a code). The account page no longer auto-refreshes.
Tried Minecraft again and it now worked. On my phone I had to enter the password after scanning the QR code from the PS5 screen.
I also had this issue with my son's MS account on a PS5.
Like others we were seeing the continous refreshing loop when trying to sign in at https://accounts.microsoft.com
I went to the additional security options page (https://account.live.com/proofs/manage/additional) (was able to sign in to this fine by getting a code sent to my son's email) and on this page selected the Change Password option.
I don't remember previously having set a password for this account so it's possible it was set up as passwordless. Now when I sign in at https://accounts.microsoft.com I use a password (the first time after changing the password I had to select the option on the sign in page to use a password rather than sending a code). The account page no longer auto-refreshes.
Tried Minecraft again and it now worked. On my phone I had to enter the password after scanning the QR code from the PS5 screen.