where are these ps % coming from?

i saw some (many) posts on reddit regarding ps plagiarism and they get numbers like 4% X% etc on ucas but where is it?? i dont see anything

Where is what?

In the post they mention something like UCAS track, i can’t find it anywhere so not sure

If a PS is identified by the UCAS 'Copycatch' plagiarism software, a report goes to that applicant's Universities with a % plagiarism score. Its up to those Unis what they do next. Applicants will also be informed about this score. 'UCAS Track' is the old name for UCAS Hub - ie. the front end of UCAS that applicants see.
Relevant info
How to avoid plagiarism when writing your personal statement - The Uni Guide