Hi SDF

"Metals" in a cosmochemistry sense are any element other than Hydrogen and Helium - and generally low mass stars only make carbon/oxygen as fusion end products. White dwarfs will be predominantly a mix of the two. Higher atomic mass products come from core processes in high mass stars - but they are extremely rare in a number sense. Their cores make elements up to iron BUT past iron fusion is endothermic and can only be powered by gravitational collapse and/or shock-wave processes - so every element past ~ 26 is either from supernova detonation waves ramming lower elements together or through radioactive decay and/or neutron capture of those ram-created elements.

Because iron is typically formed in the very core of a supernova you'd think it would all collapse into the neutron star/black hole formed by the star's collapse. A lot of it does, but a non-fusing iron core is wrapped in layers of unfused lighter elements, which are thus ready to be slammed into each other by the detonation wave. Thus a humungous amount of iron is made by supernova - and why iron is ~ 40% of the Earth's mass.

But a very large fraction of unfused hydro-helium is blasted back into the universe - an 8 solar mass supernova progenitor only collapses into a 1.44 solar mass neutron star, with the rest spread out to spike more star formation around it. Far more numerous lower mass stars will "trap" that H/He into their proportionately larger cores - the lowest mass stars will fuse ~ 98% of their mass into helium and return next to none to the interstellar medium. Above ~ 30% of a solar mass and a helium core can collapse sufficiently to burn into carbon/oxygen/nitrogen - but fusion energy supplied by this is much lower than for hydrogen fusion. Our Sun's core hydrogen will provide about ~ 12.5 billion years of light at current levels, even tho it's only 75% of the mass to start with. Helium will burn at x50 current levels for just 0.1 billion years - 5 gigayears current luminosity at 100% concentration - only about ~ 20% the energy from hydrogen. Fusing three He to make carbon creates even less energy, and making magnesium out of carbon makes even less. Most stars (~99%) aren't heavy enough to get past CNO. Much of their outer layers are blown away by helium fusion explosions once their core collapses. But a lot of CNO ends up as white dwarf stars.

So in the end much of the Universe will be locked up uselessly as either helium dwarfs, or as CNO crystal lattices in white-dwarfs. I suspect that will allow intelligence to use induced proton-decay to make energy - the proton-decay efficiency of space-time flaws like monopoles increases with the density of the feed-stock. What intelligence will use as a substrate in long aeons of induced proton-decay is left as exercise for the reader...