Your total score is what matters, not how many under or over par you are.
Not all courses have the same par.
Four under par (par 72) on St. Andrews is a 68. Four under par on a course that has a par of 70 would be a 66.
Thus 4 under par is a variable number that is relative to the par of the course played.
FWIW - We don't have a handicap. We have a scoring average. The 2 are very different.
Apparently WGT does not state par for each course - except on the scorecard. Par for each course is not information provided in the WGT Community > Golf Courses section of the website.