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https://www.abc.net.au/news/2020-05-28/astronomers-find-universe-missing-matter/12291788

So it wasn't enough that ninety five percent of the universe is made of stuff (dark matter and dark energy that does not interact with electromagnetic waves and can only be detected by gravity) that we have no idea what it is.  Half of the normal "baryonic" matter was missing as well, but now it has finally been located.

By carefully analyzing some of the recently discovered fast radio bursts (FRBs) using a vast array of instruments, it was possible to measure the matter that lies dispersed between galaxies. Even with a density of less than one atom per cubic metre, it still adds up to a lot of matter and it accounts for all the rest of the normal matter that should be present in the universe according to other well established theories.