Icon Preview is described as 'Preview how your macOS app icon will look in the Dock and how your menu bar item icon will appear' and is an app. There are 2 alternatives to Icon Preview for Linux, KDE Plasma, Flathub and Flatpak. The best Icon Preview alternative is Icon Explorer, which is both free and Open Source.
Icon Explorer allows artists and developers to preview and pick icons. Icon Explorer attempts to render the icons exactly as they would look drawn in the application. It allows to filter based on category and name.
Ikona is a companion application to a vector editor like Inkscape, providing utilities for wrangling with icons and an icon preview.
Germany
EU