Important!

I'm on day 3 of not being able to run the game. I fully uninstalled and reinstalled the game on Steam, same result.

Same issue here, with the technical cause. The client cancels each download at exactly 20 seconds (visible in Player.log as "Max 20,000.40" latency) while running ~100 downloads at once, so on slower connections each one gets too little bandwidth to finish in time — even files under 2 MB fail. And because failed downloads restart from zero instead of resuming, retrying never recovers; the remaining total just freezes. I downloaded the same files with a normal download manager on the same connection and all completed fine. Fix: resumable downloads (HTTP Range) and a progress-based timeout. I've also filed a support ticket with the full log.