This is really a matter of preference. Xbox Series X|S consoles can easily handle 4K and so getting a capture card that also supports 4K passthrough makes sense if you want to stay current and provide a better audience viewing experience. However, capture cards that support 4K tend to be a lot more expensive. If you're budget conscious then it might be best to skip out on 4K for now, but if you want your recordings and streams to really look good then get a 4K capture card.