iPhone 13 Pro Max bugs after IOS 18 update

My iPhone 13 Pro Max is not a new one, but it always was perfect. A couple of days ago it started flickering with whites lines in the bottom.

• I reboot phone several times;
• took off case
• took off screen glass
• Deleted a lot of apps I really need to work with
• reboot settings

NOTHING HELPS! Now I lost most of my passwords and settings I liked and my phone is a half dead.

I am really disappointed with IOS last update and would like to downgrade the version to previous one, but it is impossible!

i don’t want to buy a new mobile because of Apple’s developers, who might think, that all customers can buy 1-1,5k € phones every year and just didn’t care about previous models. So give us a a possibility to use previous iOS versions in official way.

is there any way to solve it??