Box on iPad screen when open it

Hi Fang314, thank you for posting in Apple Support Communities.

Can I suggest that you update to the latest iPadOS which is 15.3 (if you have not done this already) as updates can help resolve some problems. The following link can help you:

https://support.apple.com/en-au/HT204204

Can I also confirm that you have turned off 'Assistive Touch' on your iPad which is the cause of the box on my iPad.

Can I then suggest you do a 'Force Restart' as that sometimes resolves issues as per the following link:

https://support.apple.com/en-au/guide/ipad/ipad9955c007/ipados

You may also want to consider making an appointment and have your iPad inspected at an Apple Store or AASP (Apple Authorized Service Provider). Please use this link to find one in your Country Apple – Location Selector. After going through the process, you will be given all the options available.

You can also contact Apple Support as follows:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above but also again as follows Apple – Location Selector; or
• Using the "Apple Support" app, available and downloadable from App Store.