The constant variables are the age of the author and audience with whom it resonates, not the specific changes between the two time periods.

People coming of age with the harsh realities of life will lament their loss of childhood until humanity’s final days.

I agree with your sentiment, but a possible evolution is that “the happiest time of your life” has gradually pushed younger. Young adulthood used to be that sweets spot people would be nostalgic about. You had a low skill (and low expectation) job and a cheap apartment. You got paid decently and multiple pathways for upwards mobility were available. Marriage and home ownership were obvious futures for you in the years ahead. You had the freedom of adulthood to make your own choices, without having the weight of the entire rest of your life on your shoulders. Your friends were all in similar situations. Nostalgia was around drinking too much on a beach during sunset or around a campfire in the middle of a forest. Perhaps traveling to distant destinations for simple exploration and adventure in one friend’s clapped out (and paid off) car.

Now, as in the meme posted, the “ideal” nostalgia is being under the umbrella of your parents. Your parents roof. Your parents money. You not able to make adult choices for yourself.