The traditional model for humanist typography has been the letterforms of a right-handed scribe with a broad nib pen. Are there any humanist typefaces inspired by the letter forms of a left-handed scribe with a broad nib pen?
This answer may sound like I am not answering your question, but I am. It's just probably not the answer you expect.
It's the angle the nib is held at that makes the strokes thick or thin in hand writing/calligraphy with a broad nib - typically around 30° to 45°.
The angle of the nib doesn't depend on whether a person is right handed or left handed. I do calligraphy myself, and I'm right handed, but it wouldn't matter if I was left handed. The letters would look exactly the same. Left handers do have to hold the pen differently however to achieve the same angle. There are several techniques such as writing overhand, or rotating the paper, also strokes can be done in reverse, from bottom to top, so you aren't pushing the pen forward against itself.
There are also aids to help left handed calligraphers achieve the proper angle of the nib, such as left-oblique angled nibs, or angled pen holders, but these aren't absolutely necessary.
So, basically there would be/should be no difference in how fonts are designed, whether by left handers or right handers.
1There may be more smudges, however ;))– TetsujinJun 24, 2021 at 16:40
@Tetsujin Well there may be, but there are certainly left handed calligraphers out there. Interestingly, Arabic and Hebrew are written in reverse (from left to right) which should disadvantage right handers, but this doesn't appear to be the case. Jun 24, 2021 at 16:43
1@Tetsujin yeah, I know. But funny;) I've actually watched someone do it before in real life, I was like WTF?!, but it didn't seem to bother him at all. Jun 24, 2021 at 16:50
1i still know a few who write like that… hand above the line, aiming down, so the wrist & forearm never reach the 'current' wet line for two or three lines further down the page, giving it time to dry… even with a pencil– TetsujinJun 24, 2021 at 16:52
1@Tetsujin Found this video of a left handed calligrapher using the overhand technique and broad nib, if anyone is interested. Jun 25, 2021 at 2:15
Without prejudice to the above answer, Bringhurst does emphasise the right handedness of the terminals and letterforms which inspired humanist typography (see the illustrations in Elements of Typographic Style). A bit of internet research discloses only one typeface consciously based on a left-handed scribe, 'Left-handed Gill' a modified version of Gill Sans based on the strokes of a left-handed penman; other typefaces may well exist, but this is the only apparent one.
2Although perhaps novel and interesting, some of the letters have veered quite far from what most would consider to be the standard Latin alphabet. The backwards f I think probably makes it unusable. The majority of the letter forms are no different from a regular font. The backhand tilt of the italic is also a bit disconcerting. There maybe a reason there are few others quite like it. A good find though! Jun 24, 2021 at 17:45
@BillyKerr I agree that it's almost certainly unusable for any professional thing; I can't quite understand what the lowercase 'g' is getting at (especially because I'm left handed and my 'g's look... normal?)– user165598Jun 24, 2021 at 18:24
2Shouldn't the left handed p look like a normal q and vice versa? FWIW I'm left handed (and old enough to have learned to write with pen and ink) and IMO the whole concept is just silly. Jun 25, 2021 at 0:26