Most likely a linkage problem. Does the cylinder have any resistance when rotating? If not most certainly linkage.

Good news is these are pretty simple systems. Might just be a broken clip on the linkage.

Or, something stuck in the latch itself. Pop the door panel off and have a look. If the latch is sticky, remove it and soak it in oil, then work all the levers individually. This usually gets them working for another 5 years or so.