SnowRunner is a paid title and does not have an official "free download" for the full version and all DLC. While you may find websites claiming to offer a free version (v2023.02.28), these are typically pirated copies which carry risks of malware or lack of support for official updates and multiplayer.
The most cost-effective ways to play SnowRunner legally include: SnowRunner - Anniversary DLC - Nintendo Snowrunner Free Download (v2023.02.28 & ALL DLC)