Even if navigation is set to βfreeβ in the project settings, the final test may still be locked for your learners.
Why is that?
There is a second setting in the final test settings where you can specify whether the final test can only be taken after all pages have been clicked on. You can find these settings here:

Please adjust this option once; after that, learners will be able to access the final test even if they skipped pages earlier.
Here you will find more information about the final test settings:
Final test
Configuration options for the final test