glitch (green)

Here is a thing, I updated my mac software to mac os catallina 10.15.5. the next day, i opened my mac and as usual input my password, and then it's loading. but when the loading came to the end, suddenly i saw a glitch (green) just for a second and it came back to the loading part with black wallpaper (if nothing happen then usually when you log in, the background will be the rocky mountain with purple pinkish sky right?) and then it logged in. can you tell me how to stop the glitch?