Are backlinks still one thing in 2019?

Lately, I ran into several old buds in and around the SEO community and, without fail, when the topic was tackled by the customer management – all of them asked me if I knew a good backlink provider.

I'm afraid my initial response to the first man offended him. :RE So when the second guy asked me, I replied asking what his recent experiences were and he said that his main money sites still work well – thanks to the previous backlink work.

And here is the kicker … Several years ago, I worked with a guy with whom I developed links. He and I talked earlier in the week and he said that the series of dental sites we collaborated on in 2015 still paid too much for their respective keywords.

Asked what he's done since then, answered that things on the spot. But as the other sites on which he has done a structural SEO work are not classified, he is convinced that these are the links. I was shocked.
SEMrush

Which give? Am I too naive? Do return links always work after everything Google has done to discourage the creation of unnatural links?