They should improve the quality of food in sewers so that those who bought sex and thus reincarnated as rats and cockroaches can get a second chance in their next lives
On Windows, there is a Secure Audio Path API to prevent interception of the audio signal. Not sure if macOS has something similar, though it can prevent screenshotting of DRMed video. On Linux, any such protection is probably impossible unless Spotify requires a kernel module.
Note that the audio quality on Spotify is not very high (256kbps .ogg, I think), so anything thus recorded is going to sound lossy, especially after you recompress it a second time.
If you’re paranoid, you can convert the FLACs to WAV on an isolated computer (or VM), copy them and recompress them to FLAC or other formats. If there is a vulnerability in FLAC, it won’t persist through transcoding.