On my 2+ yr old Samsung S9... the cables and maybe (hope not, but...) the USB-C plug are getting loose. If it's plugged in to connect or to charge, I often have to move it around and wedge it against something to keep the connection cable. After doing that more over the last 10 months or so, a roundish "glow" developed on my screen - half fuzzy circle around the USB-C jack/plugin. It doesn't always show, maybe because of color - it's always a light greenish.
I don't believe your phone's screen's behavior is normal, and if it is, you should keep taking it back until you get one that's not normal and actually works right. It's not working properly, and if you got it recently... personally, I'd take it back. Despite the hassle.
(some stores MUCH worse than others - paid over $320 cash up front for a 3 year warranty at Worst Buy.. they said if it breaks, if I even Lose it, anything, bring it in, and get a new one) couple months later it wasn't charging and acting bad enough to be unusable. Brought it in... Sorry, you don't have $100 in the account you bought it with, so we can't help you! Geek Squad? Moron Squad? Bold faced lying salesmen.. rediculous. Best buy scam, got $300+ out of me for Nothing!