Blockchain.info API is not down. In fact, I've just used it to list all (~4000!) of the transactions of a Nakamoto address, which required multiple API calls to fetch all the data. So no, it's not in the water just yet.
You can verify this by asking ChatGPT to make example requests to blockchain.info in CURL or python for you to run.
Also, you don't need to sign up to use their API - most endpoints work anonymously without an API key. (Beware that they have a strict 1 request per 10 seconds limit or you can get IP banned.)
Yes, in fact the API itself works, I've realized that already. But I'm trying to run a script which uses this link:
https://api.blockchain.info/customer/signup and it's giving me a 503 error. And I think you still need XPUB key to use it for purposes I'm trying to use it for. So XPUB is also not working/impossible to acquire. Perhaps I'm wrong and you can guide me?