One photo shows how you would like your foul drain to appear. One shows a problem: waste backing up.
Is this the tip of the ice berg or nothing to worry about?
The starting point is probably to power flush the system out. If that doesn’t work then get a competent drainage contractor to conduct a CCTV scan to see if there is a more major problem.
Always investigate as soon as possible, particularly if you are in the process of buying the property, as drainage repairs can be very costly.