Solved the problem with repeatable fields inside a cpt-loop with Metabox:
You have to create a GROUP field (extension needed) first for the repeatable field.
And make this group cloneable.
Then inside the group you define the field that needs to be displayed in Bricks.
Because only groups can be choosen as Type/Source in a Bricks CPT loop (with Metabox)
Then it works 
Here are the relevant screenshots (to use it for yourself)
CPT Custom Fields setup for Group and Subfields (inside group):
CPT Group field edit screen with values:
This is how the DOM looks like:
Sub-Loop setup with Group-Field setting:
dynamic Data Field (Group subfield) inside Bricks:
This is how the result looks on FrontEnd:
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I found a youtube video that made it click in my head (maybe yours, too)
