Whenever I log into my MacBook Air 18, the loading screen will glitch out

Whenever I log into my macbook air 18, the loading screen will glitch out with a distorted image of my screen saver image or show colour vertical lines of the image. But as soon as I’m logged in, everything is back to normal. its never been dropped, and always up to date. ive only had it for a year. please help.

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