My cat started pooping outside the litter box but still pees in it. Makes no sense.

It makes more sense than it seems when you know that defecation and urination are neurologically separate behaviors in cats, and cats can develop an aversion to one without developing it to the other. The fact that she is still using the box for urination tells you she does not have a general aversion to the box itself. She has a specific aversion to defecating in it.

The most common reason for this pattern, with no medical cause found, is discomfort associated with defecation in that specific context. That can be as simple as the box feeling too small or too enclosed when she needs to posture for defecation, which requires more space than urination. It can also be related to litter depth, or to a previous experience of discomfort, even a single difficult stool, that she is now avoiding repeating in that location.

The first thing I would try is a second, larger, uncovered box with a slightly different litter depth, placed close to where she has been going on the floor. Not to move her permanently but to see whether she uses it, because that tells you whether the issue is the box size and type or whether something else is driving it. If you want to map out the full picture including her diet, her history, and what the box setup looks like in detail, the Work With Me assessment is designed to catch exactly these kinds of specific patterns.