Show last updated timestamp in posts

I've managed to display the last updated timestamp but recently the theme got updated and I lost it.
Searched the forum but I still couldn't figure it out.
I added this function https://gist.github.com/generatepress/3825ebd0c780b6021b0126c515f141e6
and css

.posted-on .updated {
    display: inline-block;
}

But it only shows last updated for some posts. Some others do not show anything.