First of all: nice to see a new logo. Good job!
I want to inquire about the choice of color. If we take a look at the first run experience, not only are we witnessing a clash between the blue UI color and the eyesore that is the default VSCode status bar, but now there's the VSCodium brand color slammed in there as well. The old logo harmonized completely with the blue UI color. What was the reasoning behind this choice?

I also want to inquire about the empty screen logo variation. A flat version like this would need a counterpart for what the folding shadow does on the main logo.

Maybe mostly related to this issue (though I can make a new one if you like;) the logo color clashes / fades a bit with lighter colors behind it:

Subjectively, I do like the logo, though perhaps not so much the color. Objectively, a border around it (or some other adjustment) would perhaps make it fit in better.
I would add that it looks a bit oversized when sitting close to other rounded icons (at least in the dock of macOS Catalina).

Regarding the color, I guess it's a matter of taste. But I also have the impression that it looks very bright on dark backgrounds, while it tends to fade away over grayish backgrounds.

The previous logo was 1,000,000 times better than whatever this new one is.
You can check #481 if you want a blue version of the new logo.
Honestly, now that I've image googled "codium" I really don't see why the old brand mark was discarded. It fits beautifully.
Imo older logo was WAY WAY better.
I really like the new logo, and I think it helps to differentiate/set expectations for the experience since the extensions provider was changed.
I don't really care about the color, but the shape itself is pleasing.
The new logo is bad because it's not resting on a background. This is a design feature of both Mac, Windows and Android style-guides, which can be found here:
The only noticeable exception is Linux, who by it's nature of free market competition has competing standards.
_It's worth noting that GNOME doesn't care about backgrounds, but they do care about shapes, which is also nice to read about._
In the image posted by @olivier-manomano you can see how other applications follow the style guide on Mac.
What to do
Two options if you ask me
Controversy?
In another issue (https://github.com/VSCodium/vscodium/issues/472), the project leaders have stated that they don't want to make any changes which I think is dumb. This change is directly in conflict with multiple platform guides.
Bootnote
The icon might also really suck for colour blind people. I myself am near-sighted and without glasses, the new logo is less easy to recognize then the old logo.
Here's how the new icon looks for me...

Icon has been reverted (will be in next release). Meanwhile there's another vote to update the old icon to "Big Sur style" for Mac users in #591
Most helpful comment
The previous logo was 1,000,000 times better than whatever this new one is.