Registration & Login
XChat handles sign-in differently from most messaging apps. You do not create a separate account with a phone number or email. Instead, you sign in with your X account. If you already have one, you simply authorize login. If not, you can create an X account inside the app, again without needing a phone number.
Once you are in, enabling PIN protection right away is a smart move. The PIN adds another layer on top of your X account credentials. Even if someone gets physical access to your phone, they would still need the PIN to open your chats.
The no-phone-number model cuts both ways. On the positive side, it gives you more distance from your real-world identity. On the downside, if your X account is suspended or compromised, that may affect access to XChat as well. Account security matters more here than it does in many conventional chat apps.