It can be very small things. Personally, if games have a character creator, I can't play games as my assigned gender. Impossible. If I chose my assigned gender, I will rather not play the game at all.
Some people just like to look at cute girls. It's super common to see girl characters in Monster Hunter games for example, but I'd expect the playerbase to trend cis-male
In my (transfemme) case it was not tucking an then discovering tucking.
I was always under the impression that it doesn't matter because I'm wearing a skirt that i love and you don't see a bulge with it in any way. But I tried tucking and oh boy! It's not about the visuals but it just felt so much better. Just the feeling of being flat down there was heaven 🤤
I honestly just googled and found this guide to be pretty helpful. I'm not that good at it and don't have any stuff that is specifically designed to support tucking (e.g. a gaff) so it doesn't hold for very long but I think I might change that soon 😅
For me, it's the clothing I wear. Like when I worked out, I used to wear standard masc workout clothes. But once I discovered sporty fem fits that I look good in, I loathe whenever I have to wear my masc clothing. I like how I look with fem clothing so much more.
I also started growing my hair out and once I saw how I looked with it, I cannot go back to short hair anymore. The simple thought of going back to short hair makes me feel so dysphoric. Plus the compliments I get about my curls which certainly helps.