M4A Apple Lossless File showing as audio stream format not supported

Unfortunately, m4a is not supported in Roon. Moreover, note that M4A is not lossless but lossy. You’d do better digitising to either FLAC or AIFF, but first try renaming the file with the extension AAC.

M4A is a file extension for an audio file encoded with advanced audio coding (AAC) which is a lossy compression. M4A was generally intended as the successor to MP3, which had not been originally designed for audio only but was layer III in an MPEG 1 or 2 video files. M4A stands for MPEG 4 Audio.