it’s typically just a kind of pixel art with monospaced fonts¹. any characters you see that’s not typically shown on your keyboard (e.g a filled square) can be found in a character selection program in your OS. anything else related to texts, templating and line breaks you can probably find a program somewhere on places like crates.io or gitlab or write something of your own without much trouble.

¹ a monospaced font is a font where every letter and character has the same spacing from each other, and are the easiest to do ascii art. (ascii is just one character table, but you can also gather unicode chars all you want)