a weird specific issue with right clicking something in task manager

Hey so I don't have very much information on this stuff, I'm not the best with computer related business but I do know a little bit, and I honestly have no clue what's going on (since this isn't even my computer, it's my younger brother's and he asked me for help.) So I was wondering if anyone could help because even I'm stumped? If this is the wrong thread to post to I'm sorry please direct me to a better one, I wasn't too sure where to post this.

The issue that's being experienced is whenever something in the task manager is right clicked to show options, it keeps scrolling down through them all, kinda like if you held the down key while it was open. I unplugged the keyboard assuming that could be the issue and it didn't work, it kept going. I also discovered that the issue carries on to the settings panel and open start menu, basically everything that's not the internet, and it doesn't carry over to a few other apps he said, like Steam and Discord were not affected by it.
We also ran an anti-virus which didn't detect anything, but from what he described to me he downloaded things and I honestly don't know how trust worthy the anti-virus is (again, I'm kind of an idiot when it comes to computer related stuff, so it could be a good one and I'm just being skeptical.)

So the one thing I can rule out is it being a stuck key or keyboard issue, since it kept happening once it was unplugged. And maybe if the anti-virus is right and not flimsy, it's probably not a virus, but like I said I'm skeptical of it. I really can't find much on the subject, be it because I'm not entirely sure what to look up word for word, or this hasn't happened to many people, I'm not sure which. But thanks to anyone who reads this and has any information at all, any recommendations or such, thanks again so much! :)

Try the same thing in safemode, sounds as though there may be a small element of Malware going on :)