[zserge]

A while ago I created an even smaller typeface (2x3) but that is barely readable without memorising certain glyphs:

https://zserge.com/posts/tiny-font/

[zozbot234]

The 2x3 case is very interesting though, because it's the basic size of a Braille cell. (2x4 Braille also exists, but it does not help readability all that much here.) So you could read this font on a Braille device without knowing the actual Braille script.

Louis Braille actually invented his own 10px bitmap font for mixed visual-tactile use: https://en.wikipedia.org/wiki/Decapoint It fell out of use after typewriters were introduced.

[navane]

If anything it shows a lower bound; 2x3 does not provide legible letters.