My understanding is that in models where time began at the Big Bang space typically also began concurrently. Before this time (harhar) there was nothing, but that’s meaningless because time also didn’t exist. It’s immeasurable before a certain point. Likewise space began at that time and expanded to fill all space rapidly, which I’m often a little unclear here, but my understanding is in a similar way to how space expands today outside of galaxies by space simply expanding from within itself (I.e., without force or movement). This conceptualization might help quiet that discontinuity discomfort.

I’ll search for it but PBS Space time has some wonderful intuition building visualizations and explanations in some of their parts on models for the beginning of the universe. If I can find the ones I’m thinking of I’ll edit later, but regardless I find their background material on “wtf” re: physics can be helpful.