SDDC Manager GUI:
The 'admin' user on NSX-T Edge nodes has an expired password. This can be confirmed by opening an SSH session and logging in to the Edge nodes.
Update the expired password on the NSX-T Edge nodes. After updating, set the password back to the original value via the "set user admin" command. Optionally, the password expiration policy can be adjusted afterwards.
More information regarding password management can be found in the below document.