I'm a firm believer in no cheering in the press box. But I also understand that bias inevitably creeps in because we are all human beings. If you take a job somewhere and aren't remotely a fan of the team you cover, eventually you form relationships with the individuals involved. Maybe you connect really well with the linemen or hit it off with the coach.
Even by staying completely professional, you're going to eventually be in a position where a part of you will want them to succeed, just on a human level. Or, if they get fired, it's going to impact you more than if it was someone you never met.
We all have biases. The key is either disclosing those biases (dropping "AT&T WarnerMedia is the parent company of CNN" in news report by the cable network, for example) or by having checks in place to ensure bias doesn't color the story.
Unfortunately, with more and more cuts to newsrooms, those checks are disappearing.
I think you can grow up a Seahawks fan and still cover the team fairly. I don't think you should be cheering in the press box or wearing team gear.
Oh, and pontificating about this on social media gets you nowhere, Tom Hoffarth. The only people who care are other journalists, because all the fans can't understand how you're not a fan of the team in the first place.