I'm not sure anyone can help you more than the diagnosis video above goes through the diagnosis the slop. It tells you how and what as far as that's concerned.
The bracket the cables go through on the transmission must be solid and the clips holding the cables firmly in place.
Be sure the cable ends are secure and have no slop. The up and down bushing shown in the beginning of the video and the spring bushing at the end are all about reverse.
If you go through the entire process and nothing works then you're looking at the clutch, shift tower, syncros and transmission.
Can you get into reverse and then start the car and back up? If so then the flywheel is likely shot. If not a bushing, or shift tower issue is likely.
Seriously watch the second video I linked above and go through the whole thing. The cable bushings, especially the side to side can be your issue with reverse.
Sent from my moto g(7) power using Tapatalk