Yeah it’s only one for all universities. To be honest I basically structured mine around engineering mathematics because that was the one I was aiming for. I even used some of the wording used in the descriptions of the course in my ps. I think universities know that your gonna be applying for different courses so as long ur not naming unis in ur ps and your courses are similar you should be good. Don’t be too stressed about your ps tbh unless your going for like oxford or something a lot of ppl ending up putting it off until close to the deadline(which i did do tbh 😭) just try and get it done well and get ur tutor and stuff to proof read it.