ForNAV uses the standard Business Central formatting of dates, which by default formats the year with four digits.
However, this is different from Navision classic, where the default was two digits.
To support both, the ForNAV Designer Format Dates With ShortYear property controls whether the year should be formatted with four digits (default) or two digits:
To set this property in bulk for many reports, the ForNAV Converter has the same capability: