How do I find the total number of User Tips written?

For all users combined?

103 pages at 20 per page, but 8 for the last page, so 2048 in total by all authors, according to the User Tips index page. As this total is binary significant (2^11), I’m inclined to say that this list is probably cut off, and that there are more unlisted, but perhaps searchable with the right keywords.

For a particular user?

Go to their profile page by clicking their profile image, look under Participation, then find the number for their User Tips listed there.

E.g.:

Note that writing a User Tip page, when separately from regular forum posts, requires User Level 5 (4000 points or more). Share what you know and get recognized - Apple Support