Weird green dot in corner of screen? Doesn’t show up in screenshots. Galaxy s8+

I've noticed this weird green spot in the upper left corner of my screen for about 2 weeks now. It doesn't show up in screenshots but has a distinct shape. I don't know what it is. A Norton malware scan says my device is safe, but I don't know. Here is a link to a photo of my screen: imgur.co m/ KeZCOpj
Any and all help is appreciated. Thanks.

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