My journey continues.

Apparently, there is some trick to having the Data Panel show up in Blend for a Unity project. In the video linked above at timestamp 6:38 there is no Data Tab in the Solution Explorer, then after moving from Blend to Unity and back again, at timestamp 6:46 it magically appears.
I've added images (5 & 6) of this with descriptions to the imgur album linked above. Something is weird.

After a quick google search I found out that the Data panel is only supported in projects that target .NET Framework. I usually work in Visual Studio Code but I've checked the solution with Visual Studio 2022 and the target is correctly set to .NET Framework v4.8. I am not sure what I'm doing wrong or what happened in the video between cuts that the Data Tab magically shows up.

I really want to start using NoesisGUI and Blend for my personal prototype and start implementing it in professional projects as well but it's not making it easy. :/

Team is still coming back from GDC and will give you an answer about this as soon as possible.

Alright. Looking forward to it. Thank you. :)

Blend shows the Data panel when you have a xaml file opened with the Design view selected. But in rare occassions I found that Blend designer process fails and I need to close the xaml file and open it again in order to properly show it. Have you tried that?