If you encounter an "Unknown File Version" error when trying to run the New World game, a potential fix is to validate your game files. This is how you can do it:
After this, you will have to wait a little. The Steam client will check all the game files and will re-download them if some of them are broken. This fix should help.
Here is an official Steam Guide:
If the fix doesn't help, you may try to re-install the game entirely. Reinstallation will take much more time, but you will definitely get rid of this error.