Tail-lights are a common cause. If your car has any broken tail-lights, or if any of the tail-light fixtures have been replaced, that’d be my first guess. the fixture usually has to be sealed during replacement with a special sealant, and sometimes the installer doesn’t have the needed sealant on hand, so they mickey-mouse the job and it eventually leaks. Other than that, besides windows, the drain holes at the bottom of the doors should be checked to make sure they are open & draining. When rain water hits a door window, some of it goes down inside the door, and then it is supposed to go back out at the bottom of the door through drain holes. If those holes are blocked the water will accumulate inside the door and eventually move into the passenger compartment. If you can get a helper inside the car while you spray it with a garden hose sometimes the helper can spot where the leak is too. I used that technique on my truck a couple of months ago to successfully find a leak. I used a rain storm to do the spraying of the water, but same idea.