Sorry but not going to happen. You can't go from an Apple card to an Uber or any other cobranded card.
The only thing I have heard of an Apple card being converted to is a generic Barclay rewards card. Even that I have not heard of anytime recently, but if anything would be likely be your only option.
Yes, you can have multiple cards with Barclay, as long as you take it slow and use the card(s) you do have.
If you want a different Barclay card, apply for the one you want, and once you’re approved, call in and ask them to move the credit line from the old card to the new one and close the old one.
The old card will have to be open for 12 months before you can do this, applications for new cards should be at least 6 months apart, and you have to be using your existing cards to get approved for a new one.