Can I be denied receiving a 'Go' for a promotion board if I accidentally use gender pronouns? Should I get the IG involved?

Don't take legal advise from a comment section, but... No, seriously, that's my advice. If you think you've been unjustly discriminated against, talk to a reputable law firm. If your case has no merit, they won't waste their time on any of it. If your case appears to have merit, they'll accept it because that's literally their job, what they get paid to do. If a lawyer won't take your case (or refer you to a specialist colleague), most often it's because you don't, in fact, have a case. Taking advice here, or from any non-expert, has the potential to steer you in the wrong direction, and going in the wrong direction WILL cause you harm.

I've used this tactic several times and I've saved myself thousands of dollars and days' worth of time. Not for discrimination, but child custody, auto accidents, theft, etc.

As for your infraction, you don't describe anything in what they said that would imply a trans rights issue. "He" instead of "the soldier" has been the norm for a long time because women also serve. Back in the 80s, the Catholic nuns at my *religious* school taught us to avoid assuming genders when none is specified or strongly implied. Being a soldier, sailor, or marine doesn't imply you're a man. Being an airman reeeeealllly doesn't imply you're a man.

I am grateful that I was not still in the military when all this gender confusion started. I personally think that by catering to the delusion of the soldier and not getting them the psychiatric help they need, we do both them and the service a terrible injustice.
Addiction, anxiety, depression, PTSD, and others are all issues that are considered to require counseling. Gender dysphoria should be considered the same way.
As for promotion boards holding a minor issue that is controversial against an otherwise perfectly suitable candidate is not only unfair to the soldier being considered, but also to the service.

Well, my first response is thank Gen Cracker Jack Milley and austin for having to even be placed in a position where if you don't comply to popular or not sentences you can't be promoted. This is what the IG is for or your personal attorney.

Our country and especially the military has huge problems if political correctness runs everything. Bureaucrats pull this crap to exert power they wish they had. I'd go to the AG so faster than a construction worker on a burrito.

Those of us that served in the Army and reserve, know we were Soldiers and should always be referred to as such.
I doubt ever getting IG involved would work because the decision was made by the board, probably the president. Has nothing to do with pronouns Soldier! Lesson learned.

IG for sure.

This is nonsense. The board President had a predetermined “gotcha” question based on personal feelings. Boards aren’t supposed to be a “gotcha” moment.

Does the CoC believe this individual should be promoted? —Yes, board deems promotable if the Soldier demonstrates a reasonable level of board preparation

Rest easy for a bit. Going to the IG will label you as trouble by everyone in your unit. Don't be fooled for a second into thinking that they won't know it is you. Only so many people can fit the criteria of the complaint. They can make your life miserable. When I was an E5 I pissed off our platoon sergeant by showing the LT that we had gone the wrong way on a field training for the battalion. The next month I was move from being squad leader to machine gunner. The platoon sgt. simple smiled and told me that the machine guns needed to be in the hands of the smartest men in the platoon. I was pissed, he had the power and did nothing wrong, I got screwed and put in my place. My buddies talked me out of going over his head. In less than two months I was promoted to E6, I had been boarded, I know I would have been accused of hitting my wife or something like that If I had complained. A buddy from Ranger School had that derail his promotion to E6 because of something similar. OG Army guys know a million and one ways to screw you within the rules. It sucks and it is not right and IT IS A PART OF SERVING. Just tighten up your prep and wait for the next chance in three to six months. It will feel long but it will happen.

Your going way to deep. There are now female soldiers and your response eliminated them. "The soldier should" has nothing to do with Trans vs straight it is excluding anyone but a male soldier

Don't quit and continue to fight for that stripe and the next one too.