You need to start focusing on your victories, big or small, acknowledging them, and appreciating yourself and your capabilities.

Self-esteem building isn't just something ADHD people struggle with, whether you're ADHD or not, the process of building self-esteem tends to be the same

one step at a time, start small, push your boundaries where possible, embrace fear and realize it doesn't have to control you, and that it's natural to be nervous in new situations, by accepting that it makes it a little easier than fighting it,

and, seriously, give yourself credit where credit is due, if you succeed at something, even if it's something small like doing the dishes, praise yourself for it, tell yourself you did a good job, view it as a win, and keep winning, win more, that mentality builds positivity and self-esteem when you start paying attention to what you're capable of, and encourages a sense of determination to see what more you're capable of,

either way, the thing with approaching/talking to girls.. i'm not too great at that either, but in a broader sense, self-esteem is more than just talking to girls, it's literally the standard you hold your self too. Raise the bar, think of it like a mental workout, you can't hope to have major wins in life if you don't work your way up to it, and if you don't build it up from the lower levels, you'll lack the foundation you need to handle those more, seemingly significant uncertainties in life,

going all out and getting used to failure is another method people can recommend towards building resilience and self esteem, in the sense that you become more confident in handling failures; but positive reinforcement and self-esteem building is just as important as what's the use in handling failures and being super confident that you can handle them, when you're still holding yourself to a low standard?