I like how it looks in the Sergio UI font, but I don’t know enough about fonts to know if there’s a nicer looking option or not. I’ve always been partial to Avenir Next, but I don’t know if it’s universally available.
Four serif and six sans fonts that would go well with the Joplin logo, in my opinion. I appreciate the beauty of IBM Plex Sans, but it’s a bit too stern for what I’m associating Joplin with (I’m somewhat biased towards more friendly looking fonts). And maybe its prominent J tries to compete with the logo. Segoe UI fails the O0oIl1 test, but that doesn’t really matter in a logo. You might like the (almost) symmetry of J and l in PT Sans.
Afterthought: if you prefer something more geometrical, Futura is a good choice.
Bitter, Faustina, Asap, Fira Sans, and PT Sans can be found on Google Fonts, BTW.
Afterthought #2: I see now that other fonts mentioned above also have some in-between weigths.
Choosing a standard width like Consolas or IBM Plex Mono, or something more condensed like Iosevka or some variants of Input?
Irregularities in spacing are more conspicuous at bigger sizes (compare the Jop part with the lin part). Nice alternatives are the semi-proportional Input Sans and Input Serif fonts. Another interesting font is Monoid, that tries to smooth irregularities while still remaining non-proportional. I haven’t tested it yet. As you can see, IBM Plex Mono simply solves the problem by giving l and i king-size serifs, but the result isn’t quite satisfying though.
Iosevka and Input both have a lot of glyph and weight variants.