Hello Speducator,
Thank you for reaching out to Apple Support Communities.
Do Not Disturb is a separate focus than Driving. Verify it is not switching to driving focus automatically while in the car and that is responding to your messages:
"Turn on the Driving Focus automatically
- Go to Settings > Focus, then tap Driving.
- Tap While Driving under Turn on Automatically, then select one of these options:
- Automatically: Driving will be activated based on detected motion.
- When Connected to Car Bluetooth: Driving will be activated when your iPhone is connected to car Bluetooth devices.
- Manually: Driving can be activated manually from Control Center.
- Activate With CarPlay: Driving will be activated automatically when your iPhone is connected to CarPlay."
Additional details can be found here: Use the Driving Focus on your iPhone to concentrate on the road
If the issue persists, can you provide a few more details? Which device and OS version are you currently using? Also, which exact Focus are you using?
Cheers!