My bixby and volume not working

The buttons on this phone connect via pins on the board making a direct connection with the ribbon cable. See picture below.

Because of the design it would be difficult to damage the button cable itself. However something could be blocking it from making a good connection, or could be misaligned slightly causing the buttons to not work. It is also possible that the pins are pushed in too far (towards the board) and that is making them not get a good connection.

What I would do is take the board back out of the phone and make sure that nothing is blocking it and the pins on the board look okay. Also check that the flex cable is in the groove in the frame where it should be. Then when reassembling the phone, make sure the screws on the black plastic pieces around that area are screwed in tight (not tight enough to break something though). The black plastic shield is what holds the board down to the connects for the button.