Hello,
Looking at some Apple Support articles it does not look like you can split payments while utilizing the Apple Card Monthly Installments benefit.
“If you're approved but your credit limit isn't enough to buy a device with Apple Card Installments
You can apply for Apple Card when you buy a new iPhone, iPad, Mac, or other eligible Apple product with Apple Card Installments. If your application is approved with insufficient credit to cover the cost of the device you want to buy, you can choose a different device that's covered by your credit limit. You can also choose a different payment method or use Apple's Trade-in program.”
Another possible rout would be requesting, and being approved, for a credit limit increase before making the purchase.
How to view your available Apple Card credit details or request a credit limit increase - Apple Support
I hope this helps.