I am facing the same, Any custom installed cursor is so small in mate it's hard to see, What I've noticed is if I install xcursor and change the cursor to a custom one and put it in ~/.xresources and restart, No matter what size I put for the cursor, It may change for a brief moment when the desktop loads, After opening any app, The cursor goes small again.
!!Xcursor.size: 42
Xcursor.theme: "Nordzy-cursors"
Xcursor.size: 42px
While typing this, I have been searching for ways to solve this
I came across this website, Which mentions different ways to change the cursor. https://shallowsky.com/linux/x-cursor-themes.html
1 specific mention that catches my eye and need to try after posting this,
GTK has its own cursor theme specifier ~/.gtkrc-2.0 After viewing the file .gtkrc-2.0 in my home directory I immediately noticed. the size of the gtk-cursor-theme-size=0, I am going to change the size and restart, See if this makes a difference.
gtk-cursor-theme-name="Nordzy-cursors"
gtk-cursor-theme-size=0