"I am Viktoria."
I keep writing the name correctly but it won't accept it. "Я Вiкторiя".
You're using the Latin «i» instead of the Cyrillic «і».
Some letters might look the same (like Latin A, Cyrillic А and Greek Α) but belong to different alphabets, so they are encoded differently on the computer. Most programs would be confused if you replace Latin i with Cyrillic і, or vice versa, and Duolingo is no exception.
Unfortunately, this means you can't use a Russian keyboard layout to type Ukrainian. Check the settings of your operating system or device, there should be an option to install Ukrainian keyboard layout.