If you experienced a crash, please try the following:
1. Checking corrupt data
- Select System Settings in HOME menu
- From options to the left select Data Management
- On the right-hand side select "Manage Software," then select Witcher 3
- Select Check for Corrupt Data
2. Clearing the cache (it will not delete your save data):
- Select System Settings in HOME menu
- Choose System from the menu to the left > Formatting Options > Reset Cache
- Select the user for which you want to clear cache and follow the instructions
- Restart the console and start the game
If that sole procedure won't help, please check if loading an earlier gamesave proves helpful.
3. If the console freezes or does not respond try forcing a reboot
- Remove the console from the dock (make sure to attach the Joy-Con controllers)
- Press and hold the Power Button for at least 12 seconds to force the console to power off
- While the console is powered off, remove game cartridge and/or microSD card
- Power on the console and perform a system update
- After that attempt to start the game