iOS 12.3 includes support for AirPlay 2-enabled TVs and features a redesigned Apple TV app. This update also includes bug fixes and improvements.

AirPlay 2
- AirPlay 2 now supports sharing videos, photos, music and more from your iPhone and iPad directly to your AirPlay 2-enabled smart TV
- One tap playback automatically plays your chosen TV show or movie on the last screen you used based on time and location
- Siri Suggestions to watch movies and TV shows now include an option to AirPlay
- Intelligent suggestions are all done on-device so your personal information stays private

Apple TV app
- The Apple TV app features an all new design that highlights expertly curated collections and personalized recommendations
- Apple TV channels offer subscriptions to HBO, Showtime, Starz, and more, available to watch directly in the Apple TV app, online or off
- Subscriptions to Apple TV channels can be shared with up to six family members, with no new apps, accounts, or passwords needed
- New release movies are available to buy or rent in the Apple TV app, including the full catalog of 100,000+ movies and the largest selection of 4K HDR titles
- A new dedicated kids section helps you discover editorially-handpicked shows and movies safe for kids of all ages
- The Apple TV app can now intelligently suggest playing to the most likely Apple TVs or AirPlay 2-enabled TVs nearby

This update also includes bug fixes and improvements. This update:
- Adds the ability to follow a magazine from the Apple News+ catalog browsing view
- Apple Music’s For You tab now updates multiple times a day suggesting music based on themes like genres, artists, and moods you love
- Fixes an issue that could prevent Apple TV Remote from pausing video, controlling video, or changing volume on supported receivers
- Addresses an issue that could cause calls made using Wi-Fi calling to drop
- Fixes an issue where song information from a connected iPhone may not appear in a car’s display