SAN FRANCISCO, Oct 28 — Jury selection is expected to begin on Wednesday in Los Angeles for another landmark trial about the alleged harms of social media on young users, with Meta and, for the first time, Snap as defendants.

Thousands of lawsuits have been filed in recent years in local, state and federal courtrooms across the country with various claims about alleged harms to children and teenagers caused by social media companies.

The cases — the first of which went to trial earlier this year in Los Angeles — have taken twists and turns.

Meta and YouTube lost the first so-called bellwether case earlier this year, when a jury found them collectively liable for harming a young user known by the initials KGM, and ordered the tech companies to pay a combined $6 million penalty.