We had to cancel our adoption process due to medical complications. Is there a tax break for a "failed adoption"?

It depends.

If you meet the requirements to claim the adoption credit, even though your attempt was unsuccessful, you may still be able to claim the adoption credit.

You will make your entries into the Federal section of the program.

1. Select Deductions & Credits
2. Scroll down to All Tax Breaks and select You and Your Family
3. Select Adoption Credit
4. You will be able to add your adoptive child information in this section.   
5. On the screen titled Tell us about your child, enter as much information as you have available to you.
6. Continue through the screens and answer the questions as applicable
7. When you see the following screen titled Let us know which one applies to your adoption, be sure to select the applicable box stating Our adoption was unsuccessful.

You will also need to enter the adoption expenses your paid in 2019.  Those will be the expenses that are deductible on your 2020 income tax return.

If you are eligible for the credit, TurboTax will let you know at the end of this section.