As you have been informed many times river, it is spacetime...
and matter was not in existence at the moment of the BB.
https://einstein.stanford.edu/content/relativity/a11332.html
Can space exist by itself without matter or energy around?
No. Experiments continue to show that there is no 'space' that stands apart from space-time itself...no arena in which matter, energy and gravity operate which is not affected by matter, energy and gravity. General relativity tells us that what we call space is just another feature of the gravitational field of the universe, so space and space-time do not exist apart from the matter and energy that creates the gravitational field. This is not speculation, but sound observation.
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There are many aspects to that link river, that you could learn from if you desired.