There is no perpetual free version of Nik Collection 4. However, you can access it legally via:
: DxO offers a full-featured 30-day trial for Mac and Windows. It requires no payment details and provides unlimited access to all eight plugins. DxO Nik Collection 4 for Mac Free Download
Nik Collection 4 represented a major turning point for the suite, featuring a complete architectural rewrite of its most popular tools. There is no perpetual free version of Nik Collection 4
The suite includes eight specialized tools that function as standalone apps or plugins for Adobe Photoshop and Lightroom: Nik collection 4. What's new in this Photoshop plugin? Nik Collection 4 represented a major turning point
: If you are looking for a version that is free forever, the old "Nik Collection 2012" (v1.2.11) was made free by Google before they sold the suite to DxO. It is occasionally still available through DxO's legacy links or the Internet Archive, but it lacks years of updates and may be unstable on modern macOS versions like Ventura or Sonoma. Report: Key Features of Nik Collection 4 for Mac