Very likely. Most expedition operators require a medical screening form for Antarctica, asking about chronic conditions, surgery, medications, allergies, recent falls, pregnancy, mobility and insurance. Deadlines and review processes vary between companies. Fill it in honestly and early, because additional records, a physician review or a second opinion may be needed before you're approved.
Whether your doctor has to sign something depends on the operator. Some require a physician signature from every passenger. Others ask only when the screening form flags a condition, an age-related concern, recent surgery, pregnancy or a mobility issue.
If a signature is needed, use the operator's own form rather than a generic letter, and give your doctor the itinerary and a description of the activities. A standard fit-to-fly note often won't satisfy an expedition cruise medical review, because the question isn't whether you can sit on a plane.
Nothing here means you are or aren't fit to travel. That's a conversation between you, your doctor and the operator's medical team, and we won't get in the middle of it. What we will do is get you the right form and the right deadline.