Switch Lite with error code 2153-0321, Controls Not Working and Randomly Freezing

So I have a Switch Lite here with a few different issues.

The first was that it was coming up with error code 2153-0321 every time I tried to boot it. A quick search told me that it’s speaker related, which made sense as they would hiss and pop before the error came up, and that plugging in headphones (effectively disabling the speakers) is a good workaround. That works for me, so with headphones plugged in I can get to the main menu, but would obviously like to fix the speakers.

Once I got to the menu I found that none of the physical controls on the Switch seem to work - it doesn’t respond to analog sticks, D-pad or A, B, X, Y. I could only unlock the system (where it asks you to press the same button three times) by tapping on the touchscreen.

Beyond that, the console will freeze at random intervals. Sometimes it’s right after boot (so either just before or during the “press the same button three times” unlock process), other times it has gone for 10-15 minutes, letting me go through the menu, checking all settings, updating the system software (was on 9.2, now on 10.1) and doing a full factory reset, and even playing a game for a while (not that I could do much with only the touchscreen). At some point I realised the Home button was working but that seems to be the only one. When it freezes, pressing the power button makes it reboot.

I’ve had a quick look inside and there’s no sign of damage, liquid or otherwise, but I haven’t gone as far as removing any components yet so that’s still possible. I know this is a mess of different issues but perhaps there’s one root cause. What should I be checking/looking for as the possible cause(s) of these issues?