Unfortunate about your lack of awareness on this issue.
Yes, I did use Wikipedia, but you can also find it in hundreds of other places. Sorry if I'm not impressed by your naked assurance to the contrary. If The Athletic, USA Today, NFL.com, businessinsider.com, mlssoccer.com, espn, CNN, and Ted Lasso all use the term "offsides" then it's pretty fair game.
It's one thing to say you didn't know that both were accepted and widely used, or to say that you wish it weren't so, but it's completely foolish to say that it isn't. You have Google at your fingertips, you don't have to trust me on this.