I am trying to get values from the robot in interpreter mode using a Python script. Without RTDE support, it is not possible to get information from the robot?
No, it is not possible.
The only way to return a value to an external program is via RTDE so you have to register for the values you want to read periodically.
You could also use the Primary or Secondary interface but RTDE is much more relyable (and easier to set up).
There even is a phython script ready to use on the UR Github.