Anecdotally, games that are in Game Pass can expect to lose around 80% of its expected premium sales on Xbox. That's the figure that gets thrown around. It's less if it's a big mainstream release, but generally… look at how low Hellblade 2 charted. Or where Indiana Jones came. Or even Starfield. Game Pass clearly hurt sales of those titles on Xbox.
But… if it's a game on multiple platforms, it can be beneficial. That surge in players on one Xbox can have a strong impact on sales on PlayStation, for instance.