I mean... using the definitions here:
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I'd argue that
Rick And Morty - A Way Back Home is at least as "Open World" as, say, GTA Vice City was. They're totally different types of game, with different controls and goals and some sections are linear (excluding fail states,) but they both use Open World mechanics as opposed to strictly linear or level-based progression.
If you think Open World means you can attempt "missions" in any order you please, explore a large interconnected world/map screen, and tackle gameplay objectives in an arbitrary order, then I'd argue yes. If you think it means AAA budgets, third-person gameplay with combat and vehicle sections, and voice acting, then no.