Existential dread is a weird psychological state for people who need the psychological comfort of ultimate or external meaning, it starts with laying awake at night telling yourself "things matter" and hearing that quiet rebuttal.
"What if nothing matters".
Pulling that thread organically leads people to existentialism, they are raised to insist that life "must have meaning", and then reject it.
Existentialism is for people who were inculcated with some permutation of "god", just world phallacies, ultimate meaning, and/or a belief in a "sensible" reality and found the obvious holes.
And just like nearly any position there are strong existentialist and weak existentialist
If you are born dead, if you know nothing matters, you don't lay awake at night, you just avoid going to bed at night because "nothing matters"... and if this is really your deep down than your existential thought becomes inverted.
"What if everything really does matter."
And then you spend the rest of your life trying to push discovery and research forward. Existential dread turns into a sort of existential hope and nihilism and the most common expressions of existentialism appears to come from an arrogant place of certainty, or an emphatic wish fullfillment, or a cocksure defeatist state.
I'm just one person, I know some things but there is far more I don't know than do... so.. what if it does matters?
Pushing humanity's bounds of knowledge and having a thriving, dynamic society that can prosper and fund the pursuit of that question is perhaps the only important thing.