I mean, I feel like they put the client download front and center because the vast majority of people don't actually want to manually download their game installers. The option is still very much there for those who do and collapsible sections like that are very common in interface design, though I am not sure why yours even looks like that when mine doesn't. Either way, that is not something I'd call a dark pattern. You still get the DRM free game installed either way, so I find what you're complaining about to be such a non-issue.

Edit: Actually, upon further inspection, Hollow Knight is collapsed for me by default but none of my other games are. Who knows why, I still think it's a non-issue though and not as nefarious as you are implying.