Hey justawonderer, welcome to the boards!
This might be cliché, but the answer really is that everyone's bodies are different. What works for one person may not work for another. Exposure to mainstream sexual media—porn, written erotica, what have you—can also limit our perception of what sex looks like and dictate how sex should be. You've probably noticed this too, but sex in media often shows sex very specific ways: there's no emotional intimacy, vaginal intercourse/insertive sex is the only sexual act happening (or is framed as the most important activity or "main event"), and everyone orgasms at the same time. The same goes to masturbation: many sexual media tend to only portray folks with vulvas masturbating by inserting something into their vaginal canal, with their legs positioned in a certain way. Do you get what I mean?
There's nothing wrong with only being able to orgasm from specific movements or circumstances: if anything, your ability to identify what works for you shows how much you're attuned to your own body. If you're looking to discover new ways to make yourself feel good, you might want to lead with curiosity and not be hard on yourself. For example, whenever you try masturbating with your legs folded, what do you notice about your thoughts and feelings? How is touching yourself in that position differ from touching yourself in the position you're used to? This article can be a good reference on how to do this:
Take a Self-Love Road Trip: Let Curiosity Guide Your Masturbation. Do keep in mind that even if you've done your best to stay calm and focused while masturbating without aiming for orgasm, it might not work immediately, and that's okay. Perhaps that means the position just doesn't work for you. And when it comes to partnered sex, a good sex partner wouldn't scold or shame you for not being able to orgasm. Instead, they'll work together with you to make sex a great experience for everyone involved--with or without orgasm.
Another thing you can consider is related to my first point: what do the sexual media you engage with tell you about sex? How does it influence the words you use to talk about sex? Our article about this can be a starter:
Making Sense of Sexual Media. Do you think this is something you can do?
