chefman 6 quart air fryer sync finish mode isn't working, one side just says HOLD forever.

The HOLD display is normal. It indicates the basket with the shorter cook time is waiting to start so both finish together.

Fix: Ensure you set it correctly.

1. Prepare food and place baskets.
2. Activate Basket 1, set its time and temperature.
3. Press the Basket 2 button, set its (different) time and temperature.
4. Press the SYNC FINISH button, then press START.

The side with the longer time will start cooking immediately. The side with the shorter time will display HOLD until it automatically begins later.

If that didn't work: If HOLD persists and the other basket finishes, you likely broke the sync. Pressing the +2 MIN or HI-FRY button during cooking breaks SYNC FINISH. The SYNC FINISH LED will turn off. Avoid those buttons if you want to maintain the sync.