Don't go picking some obscure app just because a classmate uses it. Some people get into really complicated stuff and end up ditching it halfway through the year. Better to go with something that actually works on your phone and computer without a hassle.
Google Docs is probably your best bet if you want something straightforward. It syncs automatically across devices, teachers can open the document without installing anything, and you can share links without worrying about versions. OneNote also works well if you prefer something that feels more like a traditional notebook with sections and tabs, and the syncing is just as reliable. Notion is more powerful but it's harder to get started with if you don't really need it - it's for people who want everything super organized from day one.
My advice is to try Google Docs this week with one subject. Jot down a topic, open the document from your phone, from your computer, and share the link with a teacher to see how it goes. If you find you need something more structured later on, switching to OneNote is just a matter of minutes. Teachers almost always accept either of these two without any issue, so pick whichever one makes your life easier.