The most legible font is Atkinson Hyperlegible, which is free and developed by the Braille institute.

https://www.brailleinstitute.org/freefont/

I never see people using it because it's a weird hybrid between serif and sans serif, breaking many traditional design rules.

That’s the most legible font for people with impaired vision, which is a completely different concept

I'm replying to the comment saying "you need glasses" to say that the best font for people that need glasses is free.

They really aren't! I was looking at some small print earlier in low light conditions and the font does make all the difference there.