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A few users had the issue that the navigation and footer have not been available after the installation.
Solution:
Create the missing header & footer block on your own in the backend. (Please login with your admin account under /user)
Go to: /admin/structure/block/block-content
Create two blocks (Type: Main Footer & Main Navigation)
Go to: /admin/structure/block
Remove the two existing footer & navigation blocks (which your error says they don't exist) and replace them with the two you just created in the step before.
Click 'Save blocks'
Empty all caches (go to: /admin/config/development/performance)
Detailed documentation links for this action:
footer
navigation