I am using at the moment a fresh install of ROME P6 X11 x86_64 iso #4403. I booted it from a Ventoy usb flash drive as I have been doing with Cooker and ROME installs for months. I use the same password for user and root with no problems. A lot of people use the same password for first user and root, this is very common.
If you continue to have problems a few suggestions are to try a more detailed description of the problem and stick to one problem at the time not multiple issues all in the same paragraph. Also show some evidence like logs or screen shots.
So whatever the problem is with passwords should be solvable if we have enough information as to exactly, exactly, what you did.