It's not a binary. Your options aren't "totally fake" or "drive everyone away with your unvarnished personality." A period of politeness and civility and getting to know someone and letting them get to know you is good and healthy.

Advice like "just show everyone all the bits of you, all at once, without context" is a great way to stay alone forever, and attitudes like "the right people will immediately like you, so if someone doesn't love everything about you from day 1 you should cut them out of your life entirely" are toxic.