LEFT, RIGHT, MID, LEN – DAX Guide

LEFT: Returns the specified number of characters from the start of a text string.
https://dax.guide/left/

RIGHT: Returns the specified number of characters from the end of a text string.
https://dax.guide/right/

MID: Returns a string of characters from the middle of a text string, given a starting position and length.
https://dax.guide/mid/