Open the Instagram post with the comment you want to copy
Tap and hold the comment
Select Copy if the option appears
If Copy is not available, take a screenshot
Use text recognition on the screenshot to extract the comment
On iPhone, use Live Text from the screenshot
On Android, use Google Lens from the screenshot
Paste the copied comment into your desired app or note
If using Instagram on a browser, highlight the comment text and copy it with Ctrl+C or Cmd+C