Although Action Launcher 28.1 is a free launcher app, the AdaptivePack addon that is needed to have adaptive icons on Lollipop, Marshmallow, and Nougat devices is a commercial product. Its regular price tag reads US$4.99, but this week it can be acquired for 30 percent less.
https://www.notebookcheck.net/Action-Launcher-28-1-features-adaptive-icons.249240.0.html