Freshers' Week is a bit like those first few days in year 7 when everyone's testing each other out and trying to pretend they're having an amazing time while feeling lost and overwhelmed - but more so as almost no one knows others from before.
I think for someone who is used to being sociable, it can come as a bit of a shock to have to start again.
What I'd say is firstly, get to clubs. Even if they're not what you want to do, pick some that eat together, or just have fun. Silly sounding clubs can often have great social times.
But also, I was guilty of this and my dc are also guilty of this:
Don't be afraid to push in a bit. I'd assume if I heard about a group going somewhere that I wasn't invited so would think "oh they're going out" and leave it. But at this point, most people are still putting out feelers. Saying "can I come?" most of the time is absolutely fine and people are the more the merrier.
But if you self-exclude by not going because you don't think you're welcome, then firstly people don't get to know you so when they are settling in a group, you aren't on their radar, but also they'll probably assume you didn't go because you didn't want to, so won't ask another time.
And people often like to be helpful. "You're going to the library? Can I join you; I'm not sure where I'm going?" etc means people can feel good about you coming because they're helping you. Then maybe you can help them to find somewhere else.
People used to say that the people you meet in freshers are the ones you stick with. Didn't find that at all, and I don't think many people (covid years excepted) do.