Starting a new job on Thursday after 2 years as software engineer at a different company. I feel like a know no transferable (language) skills; I was mostly "the expert" of the framework at the previous company and now feel like I'm starting from scratch.
How do you handle starting a new position? Do you prepare yourself or just go and see? Am I overthinking?

📌 because i am in the same spot

What do you mean with "starting from scratch"?
Do they use a language you haven't been working with yet?
You could at least try to find out some basic information about the regular stuff they are using, so nothing regular will be total news for you. But don't overdose that as long as you have no idea where their focus lies.
As for internal stuff and company secrets, don't worry! Everyone starting there starts with the same zero-level. 😉

I should mainly use the same languages but probably at a higher/better level which I'm at yet.
I know some of the tools and libraries but not sure if it's worth investing time now...
I just feel some pressure to be able to contribute from the get-go, especially since they really wanted me for some reason (like a week from application to job offer)

Similar experience here, I got to know my tech stack in more detail after I was hired, so learned even a new (regrettable) language from scratch (VB)