> 4K (or better) monitors have long since become the choice for most of those who cares about how font rendering looks.

This is the hardware solution to something that can be solved in software. If your game is laggy, of course upgrading to a 3090 is going to help, but that doesn't mean you're solving the problem.

It can't be solved in software, due to the Nyquist limit: Sharp high-contrast edges (text) necessarily have high frequencies, and you need a high sampling rate (pixel density) to produce a good approximation of that signal. People have spent a lot of effort to push anti-aliasing techniques as far as they can go, but displays with higher pixel density are just better for displaying text.

I agree that if you are making something and your target audience will be using non-HiDPI displays, then you should actually design your thing on those displays too. But no matter how good your software is, pixel density places a limit on what you can achieve.

Pixel-perfect rendering (i.e. hinting) is needed in order to reach the Nyquist limit. By forgoing it, you're limiting yourself to an effective resolution that's only 0.7× or so the physical one,

Bitmap fonts (and hinted fonts are automatically generated bitmap fonts) are pixel art, so the Nyquist limit doesn't apply. In pixel art, the pixels are treated as little squares or rectangles, not band-limited point samples. This means you sacrifice the ability to display arbitrary shapes, but I'm not trying to reproduce printed text so I don't care.

I have perfectly sharp text on a 1080p monitor because I disable antialiasing in ~/.config/fontconfig/fonts.conf and force full hinting.

Nitpicking, but a pixel is always a point sample, not a little square. The native medium for displaying pixel art is CRT displays, where these point samples are used to control an electron gun that introduces a Gaussian blur, basically the best case for purely analog upsampling (or DAC, rather) of a pixel raster. No little squares in sight, though! What you're talking about is using pixel-perfect control to reach the Nyquist limit, as mentioned in my sibling comment.

Pixel art is defined by treating pixels as little squares. There is no single native medium for displaying pixel art. The same techniques were used for games on portable systems with LCD displays. Additionally, there are many examples of printed art using blocky pixels.

The Nyquist limit is irrelevant to pixel art, because the Nyquist limit applies only to reconstructing signals from point samples. Using pixel art on a monochrome LCD (no subpixels), I can display signals with maximum frequency limited only by the sharpness of the edges of the little squares.