yay! I reached 900 too! thanks for your tips btw KiriyamaKazuo, it helped me a lot
I reached 900 ELO, what should I learn now?

If you want, I can coach you for the next step. You have to be available for call, though, as it's rather difficult for me to communicate via message for a coaching session.
I'll address some of the points made in this thread that caught my eye:
1. Playing a longer time control: if this is an option, it can definitely help with improvement (I know it helped me). Sometimes people simply have time constraints, though.
2. "If you want to get a title, play the Ruy Lopez. Vienna is good only for fun". This is complete nonsense. Arguably, one could say you don't even need a complete repertoire to get a chess title. Assuming you do, the Vienna is a completely sound opening, and I'm sure it can be played during your whole chess career.
3. More on openings: thinking the way to go forward at the beginner level is by learning openings is a classic mistake. Your time is much better spent elsewhere.
2 that’s not what I meant. I said that since at some point you will have to change your opening since you need to put pressure on the opponent. You can play it forever but after a certain point people will know how to counter against it. If you simply just want to get a higher Elo, go for it.
If you want, I can coach you for the next step. You have to be available for call, though, as it's rather difficult for me to communicate via message for a coaching session.
I'll address some of the points made in this thread that caught my eye:
1. Playing a longer time control: if this is an option, it can definitely help with improvement (I know it helped me). Sometimes people simply have time constraints, though.
2. "If you want to get a title, play the Ruy Lopez. Vienna is good only for fun". This is complete nonsense. Arguably, one could say you don't even need a complete repertoire to get a chess title. Assuming you do, the Vienna is a completely sound opening, and I'm sure it can be played during your whole chess career.
3. More on openings: thinking the way to go forward at the beginner level is by learning openings is a classic mistake. Your time is much better spent elsewhere.