I used your image to do a Google image search of internet it shows as a Ubuntu , Gnome , Flat Remix Icon package. I think ..... I am not sure as I am no expert, but I believe you can run GTK themes and Icons on many different distros. The Gnome desktop environment ( DE ) can be used with a bunch of different Linux offerings. I would have to agree after looking again there is a Peppermint Icon in the screenshot like @igoshinpoints out. https://itsubuntu.com/top-best-7-linux-icon-themes-2018/
But Solus 4 is the Linux I use and this theme and icon pack is offered with all 3 DE's they use Budgie / Gnome / Mate .