You could be dealing with a broken or worn clutch that is not disengaging as it should. This would explain the notchy shifting. But the whining noise makes me think you could have a worn or dry throw-out bearing. This is part of the clutch that allows the clutch actuator to disengage the clutch while the engine is running. If it’s worn or it runs out of grease over time, it can start to make a shrill noise and can cause iffy shifting.

It sounds very much like your car has a problem with what’s called its clockspring. This is an electrical contact that allows the functions controlled by, or mounted on, the steering wheel to operate while still allowing the wheel to be turned. Over time, the clockspring wears and finally breaks which is almost certainly why you lost the cruise control and horn functions at the same time. It’s also why the airbag light has illuminated, as the broken connector won’t allow the computer to talk to the airbag in the steering wheel.

Most workshops will be able to replace the clockspring, but unless you’re a competent mechanic, leave it to the experts as anything to do with an airbag requires utmost care and respect. Even the experts will disconnect the car’s battery before tackling any airbag issue.

Honestly, this problem could be caused by anything from a transmission that is worn out to one that is simply low on fluid. It could even be caused by a bad earth somewhere on the car or something as simple as a blown fuse.

You need to take the vehicle to a workshop that can electronically scan the vehicle and hopefully turn up a fault code that will pin-point the problem. Without doing this, you're simply guessing at what the problem might be and will end up replacing parts you didn't need to.