If the top half of the screen is unresponsive to touch. The digitiser flex is probably damaged or screen is cracked. You could try backing up your phone and resetting your phone to factory settings. I fear you need a screen replacement , in fact I’m certain you do!.
If you want to self repair this link is the slightly easier option but more expensive.
https://www.ebay.co.uk/itm/394741082330?_nkw=Xiaomi+11t+LCD&itmmeta=01J6FV1YXN580N7HYFPBDFY7QX&hash=item5be866e8da:g:6agAAOSwyJlmVfki&itmprp=enc%3AAQAJAAAA0HoV3kP08IDx%2BKZ9MfhVJKnz0F0x2BRMg7b%2B35gwZtJA4QApDWj9jiI4uyuKa6gOfMeisafZlkAq4mIKCPeMMSpsa7%2FeBeWzS4S--D80hzFUSg1MCKB%2FUezLsUJrRWsWE5%2FFIVZbw3%2Bg09reOwib1YL7wtogyTwr00PpJ7wJtzsdxxenhBX93hsJKYVB--WUE03QPCLDYH4kCY5FuZc8zojQilVxpL3vFBBk6CbHjI7gxYR6csrudjUsgC8CesITJGt3TJiZyZ0l4lazikJ6mlA%3D%7Ctkp%3ABk9SR_Duh_uzZA
this link is cheaper screen but a slightly harder repair.
https://www.ebay.co.uk/itm/395255508235?_nkw=Xiaomi+11t+LCD&itmmeta=01J6FV1YXN0VC313FK581BZ48X&hash=item5c07106d0b:g:K2oAAOSwLXVmVfa8&itmprp=enc%3AAQAJAAAA0HoV3kP08IDx%2BKZ9MfhVJKnfWOdOqUcECJsUHGI4EVPQzjG6s3SZBhiO79n1Iv8wvMTmxx8ntehAEJgrwCP9UyRVkdzgKf0Q8w5t4gvg6cxglvGZ4uyFjfl5jKNMZTD0xFc4ym9d9HKCq9zgcKcRO6vodUhcWdnGMSgGsh1Sj%2Bx1BXQprflTSR7qA6U6Z3585%2BLvQjaMRP4rFSfM5C8M%2Bs58IHAKHpnHkwx%2BPH%2BHCwS%2B7AJ5vMXKP%2BFLAXy5hH1QfS4XmC4tQmA8kd08fsFiF34%3D%7Ctkp%3ABlBMUPDuh_uzZA
This link is for the cheaper option repair. Look up others if unsure or take to a repair shop if your not feeling it. Hope this helps.
https://youtu.be/KeDwiChTAC8?si=DfG0cj_R8qbGU5oz