In music production software, dBFS (i.e., decibels relative to full scale or full code) and dBTP (i.e., decibels relative to true peak) are both units of audio measurements used in the digital domain but the two aren't quite interchangeable. dBTP is essentially a way to gauge extra volume above 0 aka inter-sample peaks ("ISPs") that may occur during transcoding to another audio format or during playback on different systems.
For example, your DAW's level meters (or other audio software plug-ins) may read -0.1 dBFS and you might conclude there isn't anything that's going to go past that ceiling or margin but unbeknownst to you, there will be inter-sample peaks in the range of +0.5 to +2 dB because lossy codecs (i.e., AAC or MP3) clip and distort even without true peak overs since they change the waveform after conversion.
For example, your DAW's level meters (or other audio software plug-ins) may read -0.1 dBFS and you might conclude there isn't anything that's going to go past that ceiling or margin but unbeknownst to you, there will be inter-sample peaks in the range of +0.5 to +2 dB because lossy codecs (i.e., AAC or MP3) clip and distort even without true peak overs since they change the waveform after conversion.
