Version and Type of Mac

For any given application in the Mac App Store, there is information on what minimum operating system is supported by that application. So no, not all Macs and operating system versions are supported.

For instance, on High Sierra, and an older style of the Mac App Store, there is an Information section on the right-side of the Final Cut Pro X product page, and Compatibility is clearly shown as macOS 10.15.6 or later. On macOS Catalina and Big Sur, the App Store product pages are restyled and one must scroll down the product page entry to the Information section, and you click the Compatibility name to show the operating system version restrictions. Do not necessarily trust the "Works on this Mac message" before you click on it.

Final Cut Pro is available for all macs as long as they are running macOS Catalina 10.15.6 or newer.