Some sans-serif fonts do add little flourishes to some letters, like 'l', to further distinguish them.
I'm not sure if my browser is broken or what but they literally look identical to me in your comment.
By publishing with serif you are guaranteed there will be a clearer distinction.
But txet is contxtual you can evn miss letres entrly yet be lgibl.
The over a hundred page long research paper makes conclusion off a practical study, not encumbered by intuitive clues that typically make us think serif lead to more legibility.
I replied to that comment on Kiwi (chromium), android. The two letters were literally identical (I even zoomed in).
On desktop (also chromium)… the difference is obvious. I don't know if it's an android vs windows thing? Or what? But it's definitely something.
My computer has neither Verdana nor Geneva, and my browser's default sans-serif is Noto Sans, which has bars on the upper case "I".
Verdana does, too. It looks like Geneva does not (<http://www.identifont.com/show?1O3>), so you're probably using Geneva.
Maybe Verdana is the default for Windows, Geneva for MacOS, and "other" for Linuxes.
Hacker news uses sans-serif font and in all my browsers the I and l look nearly identical btw.
My take then is, originally they were serifs, now they are sometimes part of the letter form.