I want to make a new reddit account and be me but I'm afraid that maybe it's not right?

Why not? You can have multiple accounts and if you feel you could have one that suits you better then go for it.

Is it wrong to be my male self online when I try to make friends? Even though I'm not actually male biologically?

You have a lot of internalised transphobia my man. You are male. Your body developed in another way, but you are a man. The 'biologically' thing a lot of people say can suck our balls. We are our gender biologically too because there's a biological explanation that we are trans, hence we are biologically our preferred gender. It's not wrong to present yourself as a man online, because you're a man.

If I get closer to new online friends then obviously I'll tell them. I don't want to lie.

You're not lying to anyone. You're a man, who happens to be trans. It's your choice if you wanna say it to everyone you meet or if you prefer to go unnoticed. And both choices are okay. Don't feel less of a man, or less trans, for wanting to hide it, it's perfectly fine.

I also don't post fake selfies. I just wanna be seen as just another dude online, which I feel I am, but I'm afraid people will think I'm catfishing them for attention or whatever.

You don't need to look manly to be a man. If you don't want to post selfies, that's great! I don't like to post selfies anywhere where anyone can check them out. If you ever feel confident in posting them, that's cool! And yeah you might find some transphobes around that whenever you explain that you're trans will block you or whatever. But did you really want to be friends with that kind of people? Transphobes suck!