My iPhone X lost 30% battery health in a week.

Well let's take a guess. You bought an iPhone X, which had to be used and it was used a lot before you got it. iPhone X was released in 2017, 7 years ago. And if the battery in that phone has never been replaced, it was due for a battery replacement a LONG time ago. The battery is failing is what's happening. And if it fails enough, it will likely swell, destroying the phone, making it unrepairable completely. I hope you didn't pay much for an iPhone X?

The phone is in desperate need of a battery replacement at a minimum. You can schedule one at your closest Apple Store Genius Bar here --> iPhone Battery Replacement - Apple Support

You likely bought a phone with a battery that had been "boosted" to make it look good temporarily, when it was in fact in need of replacement long ago.

Check Settings > General > About. Under Parts & Service History......does it say Genuine Apple Part? If not, you still have the original battery, which should have been replaced long ago.

Return the phone for a refund.

The iPhone X will not even run iOS 17 with a good battery. You need a phone that will at least run iOS 17 and operate on 5G cellular. That would be an iPhone 12 or higher model.