My phone is switch off all time without any reason can you help me

@talha55382 place your phone into safe mode. When the phone is turned on, long press the volume down key to enter the safe mode. After entering the safe mode, the word "safe mode" will appear in the lower left corner of the phone screen. Now see if it still turns off etc. If not, then you know your issues are software related, most common are third party apps that mess with your phone. Install those and see if it works better.

If it still does the same in safe mode, that this is most likely power related. I suggest that you replace the battery. Your current battery may charge but it may not hold a charge to allow your phone to fully power on etc. Replace the battery and re-evaluate

Xiaomi Redmi Note 8 Battery Replacement

Change your battery