Hi JamesOxton,
I created an app from the template Service Desk.
On the New Ticket screen, I found a hidden card for the ID column.
On the app I created from the template, its DataCard24.
When you click Value22, you will find a function for its Default value: CountRows(Tickets)+1.
When you click the Create ticket button, the value in Value22 will be updated. As the Update function for the ID card has been set to: Value22.Text.

So you could also try to use the function CountRows(DataSource)+1 on your side to see if it will work for you.
Best regards,
Mabel Mao