Helix has built-in Tree Sitter support.

> "Move to end of the scope"

You can select the current syntax object under the cursor with alt+o and expand the selection to the enclosing syntax objects with further presses of alt+o. This moves you automatically to the end of the selected syntax object. You can use alt+b to move to the beginning of the selected syntax object.

> "insert after this expression"

Select the expression and after that you can use regular commands like a and p.