FLAC and modules are fundamentally different file formats. FLACs can be imported as samples into modules, but not as songs themselves. A FLAC file only contains a stream of audio (a sample), not note data like a module.
Searching the manual for "FLAC" will show you all the places where you can load FLAC samples.
PS: What is so difficult to understand about "No support, bug reports, feature requests via private messages - they will not be answered"? I am not your personal support assistant. If anything, reading such a PM sent to me makes me delete it instantly.