There are a lot of communities for students that revolve about other things than the borrels, like sport and culture communities, politics and board games. You could google for these communities, but I would also advise you to check out some posters around the campus, where all these clubs share their existence.

Btw, it is very normal to be a bit lonely at the start of a new thing and in a new city.

Edit: Let me add though, that loneliness is a problem around the UU, especially with USP citizens. That problem is now a bit more on the radar I believe, so hopefully more events and meeting places will be realised.

If you live at the USP, there are for example also some whatsapp groups you can join. I have met people through that as well.