How do I play characters who are very different from myself?

You can build characters now, and that craft is real. The ones far from you still elude you because it is genuinely harder to inhabit a person whose life you have not lived. When there is little of you to draw on, the usual shortcuts fail. That difficulty is not a limit on your talent. It is the frontier of it. A character far from you is not reached by pretending. It is reached by finding the small human thing you do share underneath the differences. You may never have lived their circumstances, but you know fear, longing, pride, shame. Start from the feeling you both understand and build outward from there, letting research and imagination fill the rest. With your next distant role, hunt for the one true point of connection, the moment where you would feel what they feel even if you would never do what they do. Anchor the whole character there. From that honest seed, the parts that are not you become believable, because they are growing from something real.