Why Spotify/Apple Music tracks are off-limits
No matter how short the sample: commercial tracks without a separate licence trigger Content ID hits. On Instagram/TikTok that leads to muting at best and an account suspension at worst. On marketplaces the listing is rejected.
Royalty-free vs GEMA-free
Royalty-free means: licensed once, usable as often as you like. GEMA-free means: no GEMA fee due in Germany. Both have to come together for the track to be safe for marketplaces.