Everything which is now, ever was, and ever will BE (i.e. exist) commenced with and is contained by and within the Big Bang (leaving aside the problems above).
You do not know this, and I suspect you know that you do not know. The universe you can see may be a bubble embedded in some larger (presumably infinite) cosmos. But you don’t know that either.
Are you dense or just stubborn? Let’s try it again.
1) “Existence” requires being in time and space.
2) That which is not being in time and space does not “exist.”
3) Being, time and space originated with the Big Bang.
4) “Prior to”; “other than” ; “outside of” the Big Bang are categories which do not exist.
5) Ergo, your speculations about “bubbles” “imbedded” in “larger cosmos” etc. which are somehow other than the universe after the Big Bang (which Einstein proved in his General Theory of Relativity is curved without a boundary), are purley imaginary ramblings, on a par with theistic superstitions, magic, fantasy, and personal gods, and may be dismissed out of hand.
So: are you a scientist or a Woo Woo?