You have your TinyDB tags and values bass ackwards.
Also, you let a .TextColor block slip in where you needed a .Text block.
See the attached attempt to correct your image using Paint.
The idea is to use 'pass' as your tag for the password, and 'user' as the tag for the user name.
The Registration screen should solicit those and store them under the aforementioned tags.
There is no need to pass them from screen to screen, just look for them in TinyDB under their proscribed tags.