"Do I add the two IRAs together?"
Yes, when TurboTax asks for the year-end balance, it's asking for the combined value of two IRAs on December 31, 2024.
The rollover of after-tax funds from the 401(k) to the traditional IRA requires an adjustment on your 2024 Form 8606. When TurboTax asks if you made nondeductible contributions to your traditional IRAs, answer Yes. Click the EasyGuide button that TurboTax presents, then, when presented with a number of boxes for different types of adjustments, enter in the box for after-tax funds from an employer plan the amount of after-tax funds rolled over. Enter this even if 2024 TurboTax asks only for after-tax amounts rolled over prior to 2024, after-tax amounts rolled over from employer plans in 2024 are to be included. TurboTax will then ask you to provide an explanation statement for this adjustment and will include the adjustment on line 2 of Form 8606.
"there was no distribution from this IRA in 2024."
It doesn't matter which IRAs the 2024 distributions cam from. All of your traditional IRAs, including the rollover IRA, are treated as one combined IRA for tax purposes.
