Aside from that Wikipedia article, where 1 source is not available and the other one is in Finnish, there's pretty much nothing online.

I googled for G4 LED tube PWM and got products that say they are G4 LED tubes that use PWM.

Pretty sure 100% of LED products sold anywhere use PWM if you don't use them at full brightness. I sometimes walk around lightning stores with a slo mo camera and see PWM in every price bracket.

It is always PWM under the hood, the question is, how much was spent (or not) on the filtering network out of the PWM. Is it closer to buck converter or is it straight up flicker at the output.

Since these things have lots of LEDs, my first thought was to put a range of different tiny delays on them to induce destructive interference, so that the off parts of one LED's flicker are the on parts of another, to smooth out the overall output.

Actually that's not true, my first thought was "just use a layer of phosphor excited by the LEDs", but fluorescent tubes do that and people used to make the same complaints about flicker, so.

Looks like "flicker index" is a useful(?) search term, anyway.