I have long had a theory for why Stadia handled CP77 so well compared to the other platforms. CDPRs management of CP77s development was, to put it mildly, less than ideal and any extensive period of crunch will always come at the detriment of the employer's health (both mental and physical) and the quality of the end product. Personally, I always view crunch on any project as a failure, most often by management.
CDPR higher-ups though, in large part fueled by experiences with similar situations that lead to success in the past[0], were unconcerned by. If the situation had stayed similar to The Witcher 3s last few months of development, CP77 would have potentially still released in a less than perfect state (considering W3s bugs at launch, new technology, more SKUs, less dev time overall and any form of crunch, in my opinion, being a failure in itself), but likely not nearly as bad as what we ended up getting. COVID-19 happened though, as we all know, and that had its fair share of consequences for everyone and everything involved.
What I'd like to focus on are dev kits. PC gaming has the up- and downsides that come with flexible hardware choices, leading to consoles generally having more targeted optimization and often receiving more testing. But when dev kits are inaccessible due to agreements with manufacturers, those become impossible.
Stadia though, for all its flaws, had two key advantages in the work-from-home world. Whilst physical devkits exist for Stadia, they also offered the ability to access development environments via the internet[1]. Because Stadia was a targeted platform with one specific, testable hardware configuration (like a console), but allowed development and QA from anywhere with a decent internet connection, that likely explains why the Stadia version at launch was more playable and stable than any console SKU or PC experience.
There was, as far as I know, never any public confirmation of this speculation and as Stadia has seized to be, we will likely never know, but this always seemed like a reasonable assumption to me.
[0] https://www.eurogamer.net/cd-projekt-red-this-approach-to-ma...
[1] https://developers.google.com/stadia-dev/cloud-identity-gsui...