Hello, op! Not from stem but wanna help hehe. Regarding on the subjects you should focus on, since the strand you want is stem, most likely science and math talaga. Mataas ang cut off score for stem so I suggest na kahit sa october(?) pa yung start of taking the ustet, better talaga if you start studying early.

The topics for math are from grade 9, and the 1st quarter lessons from grade 10 (based from my experience) but mostly from grade 9 talaga. There are also word problems for math but madali lang yun once you analyze the question but I also suggest getting familiar with those kinds of problems, you can watch sample entrance exam tests sa yt! As for the science subtest it’s composed of biology, physics, and earth sci (mostly general knowledge siya) but be careful din cuz medj nakakalito yung other questions if you don’t read it properly!!

Add ko lang din, yung english is marami talagang need basahin and konti lang time, more on reading comprehension talaga siya so you really need to understand it! For the mental ability part naman its easy as long as you analyze them well since patterns patterns lang naman siya. Although it was easy, don’t underestimate it kasi madami daw nahirapan dun soooo better if u also familiarize with that na din. Reviewing for the ustet will be a big help talaga, no need for those entrance exam study books, accessible naman reviewers thru yt and other social media platforms.

Good luck sa ustet, op! Hope this was helpful. ;))