This is not an issue, we don't need to fix this. This is the default behaviour of Drupal popup.
Steps To Recreate:
1) Navigate to Add new comment box
2) Tap on Upload image link from comment section
3) Observe
Expected: The popup should be within the body part
Actual: The pop up overlaps with the header menu
Closed: won't fix
1.0
User interface
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
This is not an issue, we don't need to fix this. This is the default behaviour of Drupal popup.