Won’t argue for or against shoes or a specific dress code. But unions publish jumpseat guides and the info is readily available for every alpa member and even nonalpa unions publish the info for their members. It’s a courtesy and a privilege not a right. Even if you’re not visible for 99% of the flight I can’t tell you how many times I grab my bag and walk off the flight deck waiting for a gap being thanked by pax. They assume if you’re up there you’re flying or part of the crew. You represent to some degree the crew and company you’re flying with. Don’t show up and put the captain in an awkward position of having to choose to break with company jumpseat policy and telling you to kick rocks. Just be polite and in at least whatever minimum professional attire required.