Audacity is a cross-platform app that runs on (at least) Linux, macOS and windows (I suspect most other *nixes are supported to).
Also, note that most creative apps (music, video, art) do not follow the UI guidelines for any particular OS platform (partly because they tend to be cross-platform, partly because their needs are very different from office productivity and communications apps. This is true even when the apps are nominally made by Apple for Apple (see Logic Pro or FCP for examples).
Finally, Tantacrul has zero responsibility for the UI appearance of the Audacity that Wavacity is based on.
Also, note that most creative apps (music, video, art) do not follow the UI guidelines for any particular OS platform (partly because they tend to be cross-platform, partly because their needs are very different from office productivity and communications apps. This is true even when the apps are nominally made by Apple for Apple (see Logic Pro or FCP for examples).
Finally, Tantacrul has zero responsibility for the UI appearance of the Audacity that Wavacity is based on.