Hi @analytics_union and @Andrey_Osadchuk, thank you for pointing this out. I've shared a couple of options for how you can access Documentation below:
You can access Product Documentation by clicking on "Adobe Experience Cloud Learn & Support" which is listed above "Learning" and "Community" in Experience Cloud when you are not yet in a specific solution:

From there, click on "Experience League" (the center option):

Now you are in Experience League - select "Learn" at the top, and then click on "Documentation" in the drop-down menu:

(*You can access the same Experience League dropdown menu above that links to Documentation if you were to have initially selected "Learning" instead of "Adobe Experience Cloud Learn & Support" because that button links directly to Experience League)
I hope this is helpful!
Warmly,
Amelia