Appium-based framework for testing desktop app (not web)

Guys, who had experience in automating desktop applications (not web)? I need an Appium-like solution to integrate it with my mobile automation (written on Appium).

Our company has a messenger client on 3 platforms: Android, iOS and desktop. Client data is synchronized between these platforms.
We already have a basic automation for mobile platforms (using Appium). Now I need to develop automation for desktop.

I want an Appium-like solution, so it would be easy to integrate with our mobile automation.
I found WinAppDriver, but it is for Windows only. Most likely our desktop app will be cross-platform (Windows, Mac OS, Linux).

Is there any solution simular to WinAppDriver, but cross-platform?

Our desktop app is based on Electron, so probably I could test it with Spectron (it is cross-platform). But I doubt that the integration with Appium will be fine. And I thinks it’s more for developers (like Espresso for Android).