Automatic Restart

It might be a hardware (Battery? Digitizer? Screen? Other internal component? failure but we, just users like you, cannot diagnose that issue remotely, sorry.

If you already tried (to no avail) a "forced" restart of your device, as per these instructions:--> Force restart iPhone, I suggest that you 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.

Your battery has reached the critical point of its life, and might have unpredictable behavior.

Create a full backup of your iPhone as soon as possible (before the battery dies), then make an an appointment (*) and have your battery replaced at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector.

Regards

Giulio

sho69 wrote: "Yea it is original. its about 80%"

80% is not healthy and is probably the reason for the restarts. Have the weak, aging 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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sho ~ Does your iPhone 11 still have its original battery?

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

Settings > Battery > Battery Health & Charging

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