My guess is that this might actually be a earphone cable problem. If the earphone cable is damaged in such a way that it appears to the iPod Nano that you are pressing the control button at random times, then I think that you will get this kind of behavior. I would try switching to a different set of earphones and see if it fixes the problem.
I don't think that it is possible to know whether it is fixable or destroyed without opening it up, though I lean toward destroyed. If you open it up you could remove the shield and try re-seating the connectors on the cables that go to the display/digitizer. That's the cheap fix, if it works. If re-seating the connectors doesn't work, then you either have a problem on the logic board, or the display/digitizer assembly. You could buy a display/digitizer assembly, and try that first; it's cheaper than the logic board. However, you might end up where it really is the logic board, and then you're out money for a display you didn't need, plus the cost of a logic board ($$$). This is one of those situations where you would probably be money ahead to just take it in to Apple for a flat-fee replacement.
Here’s a trick you can use if your black tri-wing screws would rather than strip than come out: the reason they’re stuck is that Apple put adhesive on the threads, and if you apply heat you can defeat the adhesive. Once I stripped the first one I realized what was going on, and I put the tip of a soldering iron on the remaining screws for two minutes. Presto, they came out easily. If you strip one like I did you can either break the plastic like Al did above, or you can use a Dremel tool with a cutting disk to cut a slot in the head of the screw, converting it into a slotted screw head. You have to judge it carefully: deep enough to get a bite on it, not so deep that you destroy the integrity of the screw. Also, you have to mask off the surgery site: I put down paper everywhere except where the screw was, then covered the paper with aluminum foil. The foil protects against the sparks created by the cutting wheel, the paper insulates the circuit board against shorting by the foil. Not for faint of heart.
The question I have is this: the 2017 iMac 21.5” had a modular CPU assembly, meaning it was socketed and could be replaced or upgraded. Does the 2019 model have this feature? Or is the processor soldered directly to the board?
Here’s a trick you can use if your black tri-wing screws would rather than strip than come out: the reason they’re stuck is that Apple put adhesive on the threads, and if you apply heat you can defeat the adhesive. Once I stripped the first one I realized what was going on, and I put the tip of a soldering iron on the remaining screws for two minutes. Presto, they came out easily. If you strip one like I did you can either break the plastic like Al did above, or you can use a Dremel tool with a cutting disk to cut a slot in the head of the screw, converting it into a slotted screw head. You have to judge it carefully: deep enough to get a bite on it, not so deep that you destroy the integrity of the screw. Also, you have to mask off the surgery site: I put down paper everywhere except where the screw was, then covered the paper with aluminum foil. The foil protects against the sparks created by the cutting wheel, the paper insulates the circuit board against shorting by the foil. Not for faint of heart.
The question I have is this: the 2017 iMac 21.5” had a modular CPU assembly, meaning it was socketed and could be replaced or upgraded. Does the 2019 model have this feature? Or is the processor soldered directly to the board?