Hi Saguaros,
I just tried to access the backend with the given login data for the support account myself. It worked just fine. May I kindly ask you to try again?
I also assigned the login page to Cassiopeia as a test. The passkey works with Cassiopeia, hence JA Blockk must be the issue. You had already solved this issue for me under Joomla 5. However, it stopped working after the update to J5.4 and T4 2.5.1.
Btw, there is no passkey configured for the support account.
Best,
Michael