Strange behaviour

If you already tried (to no avail) a "forced" restart of your X, as per these instructions:--> Force restart iPhone – Apple Support, something could have gone wrong during the latest update procedure.

I would try to install a fresh copy of iOS/iPadOS. To do this, create a full backup of your iPhone/iPad (1), then restore it to factory settings (you need a computer to perform this step) and, in the end, set it up as new (2).

When done, restore data from your previously made backup (3).

Follow the instructions provided in these support articles:

(1) How to back up your iPhone, iPad, and iPod touch – Apple Support

(2) Restore your iPhone, iPad, or iPod to factory settings – Apple Support

(3) Restore your iPhone, iPad, or iPod touch from a backup

If the issue still persists, contact Apple Support directly using this link:--> Get Support or, even better, make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

anirudh ~ What version of iOS is your iPhone X running?...

Settings > General > About > Software Version

Does it still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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anirudh25 wrote: "I have iOS 15.5 on my phone and have 80% battery capacity. I have been using the phone from last 4 years."

80% is not healthy and is to be expected in a 4 year-old battery. The long process of applying an iOS update to an old iPhone with a weak battery can be the proverbial "straw that broke the camel's back." ...So have the battery replaced and all will be well:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

(Articles found by searching Apple's Knowledge Base.)

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