For an explanation about the impossibility of straight-line infinity refer to: “Straight-line distance infinity analysis”.
Having already established that straight-line infinity cannot exist, it follows that there must be an outer limit/boundary to spacetime (the entire cosmos; universe), i.e., spacetime exists as a totality; a finite volume.
Obviously, it is impossible to fit an infinite amount of anything into a finite space.
“Big Bang & Creation Myths” – produced by: “The Institute of Art and Ideas”
Regardless of whether a supposed infinite number of pocket (also known as "bubbles") universes form from a single point (singularity), or materialise evenly spread out in an assumed pre-existing finite volume of spacetime – the result is 1 infinitely dense region of matter.
An infinity of bubbles starting to expand from a single point will form 1 infinitely dense solid region, then as they expand they'll never actually separate.
If the number of bubbles doesn’t start out infinite (i.e., progressively increases instead), then the number will simply remain finite.
If it’s supposed that space pre-exists independently (as mentioned above) when universes start to form, and that they form to be situated evenly spread, expanding throughout the finite volume of the pre-existing cosmos – then if they start out infinite in number, the result will once again be 1 infinitely dense solid region.
If the number of pocket universes doesn’t start out infinite, then although the universes might eventually collide with one another – the number will simply remain finite.