I came here to report this same issue. This fix worked for me -- I was able to select a new DC from the World Selection drop-down menu above the character list -- but SE still needs to fix this.

I am on PS5 too. When I log out on Materia and I try to change data centers by choosing Data Center from the title screen, the cursor on the Data Center Selection screen is in the wrong place. Normally it points to the regions -- "NORTH AMERICAN DATA CENTERS," "EUROPEAN DATA CENTERS," "JAPANESE DATA CENTER," "OCEANIAN DATA CENTER." When I am logged out on Materia, the cursor is lower and indented, pointing between the second and third data centers in the list (between Crystal and Dynamis in NA, for instance). I can move the cursor back and forth between the different regions using the directional arrows on the gamepad, but nothing happens when I press X to select one. So far as I can tell, the Data Center Selection screen works just fine except when logged out on the Oceanic servers.