Existentialism produced a lot of interesting philosophy and it had much to say about philosophy as a way of life.
But it seems to me the core insight of existentialism is mistaken. Existentialism got its purchase from the insight that the death of God (Nietzsche, Heidegger) or the loss of metaphysical foundations for human existence (Camus), or the inherent capacity of human consciousness to negate (Sartre) means that contemporary human beings suffer from a loss of meaning. Human life is inherently absurd. As Camus wrote:
The absurd is born of this confrontation between the human need and the unreasonable silence of the world.
This is implausible because many non-believers lead meaningful lives and few non-philosophers spend much time worrying about absent foundations.
This is not to say that human beings don’t suffer from a loss of meaning. We surely do, but its source is in the degrading conditions of an individual’s life.
If the meaning in one’s life comes from a relationship, and it is collapsing, one might suffer a loss of meaning. If your choice of career is no longer satisfying, then a loss of meaning or purpose might ensue. If your life doesn’t live up to your expectations, life will seem meaningless.
Putting aside cases of clinical depression, loss of meaning isn’t generally global or metaphysical. It attaches to specific actions and our ability to make them intelligible, a misalignment between one’s actions and the meanings they are supposed to have.
The solution isn’t to manufacture meaning out of thin air but to become more attuned to your environment and your real desires.