Obligatory: the most accessible font is usually a font your readers are already familiar with. This font looks distinctive, and personally I kinda like it, but it's not a magic wand you can wave over a document to make it more accessible.
The default font needs to be dyslexic friendly on a dyslexic's computer if it's not already, and it should be the OS's job to ensure this.
I am afraid there's no one size fits all wrt fonts and accessibility because I suspect different conditions have different requirements, so you can't pick yourself as a web designer.
We indeed need dyslexic friendly fonts among others so dyslexic people can configure their devices with one that they like, fonts that are indeed actually proven as being effective as another commenter said. No proof: it didn't happen.
I think sans serif fonts are preferred for most screen reading because it takes effort to perceive the tiny serif details, or just the really thin lines like the horizontal in the 'e', at typical font sizes.
But there are no absolutes so fonts that try to be more legible use some tails and such to make characters distinguishable.
With screens becoming more precise, it may be less of an issue, serifs and especially horrible on low definition screens, but it's not clear they improve things on higher definition screens.