Sorry, I am not posting here to contradict you. Just want, to clarify better some parts of it.
Im afraid I have some good news and some bad news about that. The good news is, that it is not related to the polish of the actual game. BG3 looks absolutely crisp on the Steam and GOG version. Sure, it certainly needs some more tinkering with popping in textures etc. but that more related to driver optimization (not an expert on that, though. So don't quote me on it)
This problem comparation you are making doesn't apply for streaming service. ESO for example had exactly the same problem when it lunched in Stadia. Now it looks beautiful and crispy. As per my post above, blurriness will always happen when the game is not optimized well for Stadia. This is not related to the pc version of the game, it is about polishing the Stadia version to a framarate that doesn't impair the video encoding process. Also the game is running much better using DirectX 11 for now, even though Laurian studio is recommending Vulcan. It's just a older and easier API to use. Stadia API is Vulcan only, and it is harder to use because is newer for many developers.
Im The bad news is that it is a well known issue with Stadia. Specifically with Stadia on PC. This blurriness and the movement pixelation also occurs in many other games on Stadia. It is not connected to your bandwidth. If you have the chance, use Stadia on your TV. For some reason it works well on every other Stadia option than in the Browser on PC. Even worse is, that it could be related to a lot of different issues that - generally speaking - are all solvable. For a little more clarification of the search for the problem, you could read this post:
Chrome Quality IssuesThat is actually a different problem. The link you posted is talking about some possible Network performance and Google Chrome Browser issues. Most of these blurriness are caused by lag on the user end. The blurriness we are talking about is caused by rendering problems and lack of optimization. For example, I've experience lag using Stadia because a issue with Nvidia cards drivers and Vsync in the Chrome Browser, but this is not related to BG3 current problem. If you have any problem like that, let me know and I can help you to solve it.
Im If these fixes dont help, I highly suggest using the Stadia+ Extension in Chrome. With this, you can force 4k, change the stream decoding, or simply use and overlay to monitor your connection, FPS etc. It even adds a search bar to the Stadia homepage (weird that Google didnt do this in the first place). Here is a link to Stadia+
Chrome Web Store: Stadia+ ExtensionThat wouldn't be a solution for this problem because Stadia needs VP9 hardware acceleration to works in 4K. Thus, forcing VP9 in this case would not change anything. Additionally, that could become a huge problem for who does have a older hardware that does not support VP9 hardware decoding. It would only increase drastically their input lag. That is because the streaming will be decoded in a software level and not hardware anymore.
Before doing as you recommended I would suggest to check if your computer has hardware VP9 decoding by typing chrome://gpu in your address bar. If you find hardware VP9 decoding available there in the list and you don't have a 4k monitor, that is a great suggestion to improve the image quality. Otherwise I wouldn't recommend to do it.
Sorry again if it sounds like I am being harsh on you. My intentions here is just to help people understand better how this technology works.
Hope this helps and I am always here to help troubleshooting any problems you might have with Stadia.