I use the free software Krita for digital painting. With it there is a very useful and simple way to create tiles. So here is my little tutorial/post mortem that show how I made tiles in my entry.

2a = activate manualy the wrap mode: View menu> Wrap around mode OR 2b = Create a shortcut for the wrap around mode: add the shortcut in Settings> Configure Krita> Keyboard Shortcuts (search for"wrap")

This will show the image as if tiled orthographically. Don't forget to create a canvas with the drawing only. Like that you will able later to block the alpha channel and replace the black color of the drawing with other colors

resized tile

Original tiles (of Lastcrifices: my jam entry)