Why is my Ipad restarting itself

Without detailed information as to circumstances, or patterns of usage that may contribute to a spontaneous restart, diagnosis of the cause is difficult.

You might be best advised to seek assistance directly from Apple Support - who have the ability to run remote diagnostic tests and/or review performance log files. You will find the Get Support link at top-right of this page. Alternatively, you can open a support case using the excellent Apple Support App; if not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

As a further alternative, you might consider seeking diagnostic assistance from the technicians at the Genius Bar of your local Apple Store:

Genius Bar Reservation and Apple Support Options - Apple

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