How to substitute something modern for the TDA2003?
With rail to rail output, at 5V supply, we get +/- 2.5V peaks which means a non-BTL amp will only do 0.78W &quot;RMS&quot; into 4 ohms. So what you're asking isn't strictly possible without a voltage booster, but well, I'll assume 0.78W should be enough.
The type of jack connector you have tends to short when inserted or extracted, so you need a short circuit proof amplifier. TS4962 datasheet mentions it is not protected against shorts, so it wouldn't be suitable anyway.
I guess filter-free class D amps have to be BTL. If it was not BTL but had the speaker connected to GND instead then the speaker wires and voice coil would have a common mode of half the unfiltered output square wave, which would cause lots of emissions.
So you'll need a LC filter.
But you could get a class-D amp that is short circuit tolerant, like PAM8302 which is available on cheap pre-soldered modules. This one is filter-free, but nothing stops you from putting a filter on the output anyway.
If you put a capacitor in series with the speaker to block DC, I don't see why it wouldn't work with only one output connected.
If it still smokes with one output unconnected, you could try putting just the LC filter on the unconnected output, and maybe add a dummy load, as high resistor value as possible, between the outputs...