What plugin formats does FCP support?

VST, VST3, and AU audio plugins work in macOS and show up in all apps that use the system for audio work, like FCP and Logic.

Templates made with Apple Motion are compatible as long as the template is not made by a version of Motion that is NEWER than the *corresponding* version of FCP you have. (Compatibility chart). Templates created in Motion 5.0 are still compatible with the current version of Final Cut. If you're copy of FCP is older than the current version, be careful about buying more recently made templates. (It is possible, depending on the what the Motion template includes, to "backdate" a template to make it compatible with older versions of Final Cut. However, if the newer template uses/implements some type of object or process that has been added lately (like the Neon glow), then it will not be possible to backdate past the compatible version of FCP for which Neon has been available.

Motion templates that use customized programming via FxPlug are *susceptible* to failure upon software changes in Final Cut Pro and/or Mac OS updates. Many users frequently have to wait until the template maker updates their software for compatibility.

Please provide the link of the plugin you are trying to get.