>>7781790 (OP)
unironically hard round brush
make a round brush with no opacity/flow dynamics and no taper or a very slight taper, and set it to between 2-4px
do the same thing for the eraser
think of it like a gel pen
i've seen multiple ways of getting the large blocks of black when you need it
>lasso select + fill, further refine with eraser
>increase pen size to roughly what you need + shape using eraser
>>7781806
this could be eraser artifacts or actual tapering. these details are trivial though and most won't notice or care. with or without a taper will get you roughly the same line when you're working with lines that small, so long as you have flow/opacity dynamics disable (the more important thing)
also gotta keep in mind that aliasing can be an issue on certain screens with lines that thin on a high contrast white background, so a line without a taper can look like its tapering and vice versa at certain resolutions
fwiw i think op's brush has a slight taper, but again, i don't think it matters that much