For those specifically interested in FIFA 19 on the Switch, there are additional technical considerations:
Downloading an NSP file of FIFA 19 from an unauthorized source constitutes software piracy.
The request seems to be for educational or informational purposes. Here's a generalized response:
Instead of risking a console ban or malware infection, consider these legitimate alternatives:
One of the biggest dangers of searching for "free downloads" of NSP files is the prevalence of malware. Sites that host pirated Switch games are often unregulated and riddled with malicious advertisements.