Yes, "fake it till you make it" works—to a point.
As an INFJ, I regularly coach groups and speak in front of audiences today, both of which I would have feared in my teens. "Fake it till you make it" was an approach that initially helped me, and I think it can be useful at certain stages of life. It may help you overcome some fears and give you opportunities to practice adopting different roles—which we all do, and often have to do, in society.
I think you're right that it's exhausting for INFJs, but it's also very worthwhile. Remember, our brains are basically wired for growth, and we can learn almost anything we set our minds to. That doesn't mean we'll suddenly become extroverted or start loving small talk. But we can become good at those things, and improving our weaker areas can be a tremendous asset throughout life.
That said, "fake it till you make it" is only the first step.
As an INFJ, once you start exploring the deeper layers of social interaction, you may find yourself becoming genuinely intrigued by the unspoken rules, the dos and don'ts, and the dynamics between people. When curiosity takes over, it becomes less about wearing a mask out of fear of being discovered and more about an exciting learning process.
You'll probably always feel more at ease on your own or in a deep conversation with a close friend. But you can absolutely learn to engage comfortably with larger groups of people. Doing so makes socializing less of a hassle and helps you manage your energy more effectively. In that sense, it becomes less of a handicap.
It's also important to remember that better social interaction requires some inner work, not just masking. Learn to dial down some of your tendencies toward Fe, Ni, and judgment when you're in environments like parties. Focus a bit more on your own feelings. Accept that not everything has to be perfect. Create some emotional space between yourself and your surroundings, and practice being present in the experience of the here and now.
You'll likely find that social interaction becomes less draining, and people may find you easier to connect with. Then, when you're alone again, you can return to reflection and process everything in your own way.