Please paste the custom CSS code to “Appearance > Customize: Additional CSS”
cursor: url(the-url.svg), auto;
Notice: It supports png and SVG format.
If the mouse cursor is not shown, please check if the uploaded images size is less than 128 x 128px. Please make sure there is width and height value in SVG source code if you upload SVG format images, like: <svg width="72" height="72" ...>..</svg>