cousin_it and Vladimir_Nesov's replies are good answers; at the risk of being redundant, I'll take this point by point.

to some alien species we might encounter or AI we might build, our values would be as meaningless as the values of insects are to us.

The above is factually correct.

humanity’s values have no cosmic significance or absolute validity in our vast cosmos

The phrases "cosmic significance" and "absolute validity" are confused notions. They don't actually refer to anything in the world. For more on this kind of thing you will want to read the Reductionism Sequence.

all our creations and efforts are ultimately futile in a universe of increasing entropy and astrophysical annihilation

Our efforts would be "ultimately futile" if we were doomed to never achieve our goals, to never satisfy any of our values. If the only things we valued were things like "living for an infinite amount of time", then yes, the heat death of the universe would make all our efforts futile. But if we value things that only require finite resources, like "getting a good night's sleep tonight", then no, our efforts are not a priori futile.

Only egotism exists.

Egotism is an idea, not a thing, so it's meaningless to say that it exists or doesn't exist. You could say "Only egoists exist", but that would be false. You could also say "In the limit of perfect information and perfect rationality, all humans would be egoists", and I believe that's also false. Certainly nothing you've said implies that it's true.

The Metaethics Sequence directly addresses and dissolves the idea that everything seems to be meaningless because there is no objective, universally compelling morality. But the Reductionism Sequence should be read first.