iPhone XR is restarting again and again.

Krish ~ Unexpected restarts are a common symptom of a weak, aging battery. So have the original battery replaced:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

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

õ¿õ¬

Krish ~ 80% is not healthy and is the level at which Apple recommends replacing the battery.

õ¿õ¬

Krish ~ Does your iPhone XR still have its original battery?

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

Settings > Battery > Battery Health

õ¿õ¬