First I am not talking about images or screenshots and I doubt very few are. Granted they get used as pointers for explaining the change in graphics fidelity people refer to but most "downgrade" claims don't come from images or screenshots but from the debut trailer, VGX and SOD when you compare it to everything released after that.
Second I already made it clear that I am no graphics expert whatsoever and features that for the experts enhances graphic fidelity can be absolutely lost on me and I cannot for the life of me see what the people knowledgeable about that subject talk about when for example when Digital Foundry do compare videos on their YouTube channel.
What I can see though and what matters to me in regards to a game's graphic fidelity is the atmosphere it can present. And atmosphere means the world to me in regards to RPGs. I love dense, gritty, mature, believable and real atmosphere and enviroments and in that regard there's to me a step backwards when I compare the older material against the new material. The whole mood and atmosphere of the scenery has simply changed to a less dense, less mature, less believable and less real world.
Why that is I cannot say, as mention I am no graphic exert and therefore I cannot say: "oh they turn of that feature or remove that effect". The only real sense I have in this regard is I see a change in color palette, to a certain degree art direction, density of foiler and the light feels differently. Those things combined with properly some features and effects turned off or removed have completely changed the mood, the feel and atmosphere of the game.
And I am fully aware that this experience can be and is subjectively - absolutely - but over the many threads I have followed and participated in, in regards to this whole "downgrade" business I think I can safely said that many others feel the same. Others on the other hand like the "new look" and that's great for them. We all like different things and what does it for you doesn't necessarily do it for me.
And believe me I will still play the game, of that I am certain. I am not on that wagon that yells CDPR lied to us - burn them all. The game for sure has so many other breathtaking merits going on for it that CDPR in the future will have raised the bar in regards to how a single player RPG should be done.
But I am also sure I will look back at those three first trailers with a bittersweet feeling and feel a little sad about what in my point of view could have been in regards to the atmosphere and mood. I will feel the icing of the cake was removed.
All that of course entails that there actually have been a "downgrade" or a changed or it is as
@marcin360 answered YES to and that was that we can replicate the graphics fidelity of the earlier trailers.
We just don't know yet since Ultra hasn't been shown and they are still working on polishing the game.