Most desktop environments manage the cursor using the Xcursor library
by default; this comes with scalable or multiple-sized cursor themes.
However, when running just a simple WM (twm, bspwm, ...) the cursor
handling is left to the X server, which uses a very simple fixed bitmap
font (this is called a "core" cursor). The font is uncomfortably small
on a high DPI display and must be replaced with a saner default.
Up until recently[1] it used to be possible to change the font on the
xserver command line, however the font name is now hardcoded. It's still
possible to change it, though: here I override the `fontcursormisc`
package and set an alias that points to a vector variant of the original
cursor font. The font size is set to match the standard cursor
dimensions on a 96dpi display. It's not perfect but it's a very simple
and effective solution.
[1]: 56ea4c769c
dd38ae1f2c