This is a common comment. I suspect this has to do with the training images from Adobe Stock. Adobe Stock probably has a much higher proportion of happy/smiling images of people to frowning/sad/angry. When I have encountered this problem, I have found adding more negative words tends to pull the emotion away from happy and smiling towards sad/angry.
With free open source tools like Krita and free AI plugins it doesn't cost any credits and results are much better and easier to achieve. No reliance on external web servers to generate images either...
It is what it is. A sad, sad situation... Blonde handsome guy agrees...
I did try Firefly, so biased on safe pictures , happy people , brown people , avoiding in the hardest way any similarities to real artist's creations. It's a tool for stock photos, unsuitable for artistic creations. Any other text to AI is better and by far less censored.