Hi, Elly
The segment you need is like the following image.

The second block is a query block with the condition that the status of related leads is open.
The first block of the segment is set with a template “Submitted a form”.

Here are the submissions of the Marketing Form.

The lead F4 L4 is an open one.

Here is the result of the Segment.

If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya