Is this the dark theme that comes with Windows 11?

No. it is customized theme.

Yes, Windows 11 includes a built-in dark theme option. You can enable it through the settings menu. To do so, go to Settings > Personalization > Colors, and then select Dark under the "Choose your mode" section. This will change the overall appearance of the Windows interface to a darker color scheme, including the taskbar, Start menu, and supported apps

The default dark theme is not like this. This one has some kind of customization!

No... It is not the Default Windows 11 Dark Theme !!!
This one is customised with the help of some app...

It is pretty cool. How did you made the changes?

Answer is No. It's a customized theme. Even icons are heavily customized.

OP, do you know how to tweak the theme like this?

Looks much better than the default dark theme on Windows 11.

It seems so. It looks cool, I like it.