As of today the current 32-bit Windows version can load in ancient FileMaker Pro 7. We don't expect clients to use that, but we know that some still have 32-bit Windows and use FileMaker Pro 18 there to connect to FileMaker 18 and 19 servers.
For macOS we support currently macOS 10.9 and newer. If you need plugins folder older macOS versions or 32-bit FileMaker Pro, please let us know.
And of course we work hard to get our plugin ready for the future. MacOS Big Sur and Apple Silicon are coming sooner than later and we may need to adjust for those.