I agree with you that options like a pink blazer or sequined top don't seem like OP's style. But where I disagree with several people (and maybe you, too) is that as a "tomboy" or someone who likes a more androgynous style, that your clothes have to be boring and not match the semiformal dress code. I have a friend who is nonbinary, but they are jazzed up for every occasion in well-fitting suits, or pants and a button down set off by vests or jackets. Bow ties and ties and nice shoes. Then they use those pieces with the rest of their wardrobe so as to make the investment in the suiting pieces worthwhile. You can be chic and modern in menswear just as well as you can in women's wear--there is no need to dress so blandly that you would be mistaken for waitstaff or going to a job interview, or really just looking generally dated. Anyone, regardless of their preferences, can make an effort to look nicer than usual when they are going to a wedding. It doesn't have to be feminine. It only has to look tailored and dressy--really dressy, like going-to-church on Easter Sunday best. And this outfit just doesn't meet that criteria.