People had a lot of success buying cheap amps from AliExpress based on a known chipset, like the TPA3250 mentioned in the article, and change the few components that matter.

Usually, it is about changing the cheap knockoff caps by proper audio-grade ones.

Now you are left with the 90% of the work, that is getting a good power supply ;) The easy way is battery power, but then you need to charge the batteries. Linear power supplies are big, expensive and inefficient, but relatively easy to get right.

Switching power supplies are tricky as they tend to introduce all sorts of noise, in fact, they work almost in the same way as the amplifier itself, so you are basically powering an amplifier with an amplifier, both with their own feedback loops.