The standard advice is to offer the opposite of a video game. That is why it fails.
It is rarely "screens". It is usually one of: visible progress, competence, control over a world, or other people. A child who loves building is not the same child as one who loves competing, and offering them the same alternative will fail for one of them.
Progress: anything with a visible tracker — a chart that fills, a model that grows, a chain of paper links coming down.
Competence: a hard skill with obvious levels. Juggling. Cards. A rubik's cube. Cooking one dish properly.
Control over a world: building. Construction bricks, dens, model towns, drawing maps of imaginary places.
Other people: it was never the game. Get the friend round.
"Instead of the game" tells a child this is the worse option before they have tried it. Just start doing the thing yourself, nearby, and say nothing. It works far more often than it should.
That is a bigger question than we are qualified to answer, and the honest state of the evidence is more mixed than either side of the argument suggests. This page is about what engages a child who loves games — not a claim about harm.
Ending at a natural stopping point rather than a clock time removes most of it — many games cannot be paused without losing progress, and being made to lose progress would anger an adult too. Ask them when the next save point is and hold them to it.
Part of our guide to Retro arcade party.