I loaded same sample (Kick) in FL v20.x and Ableton Live v10.x, in FL the volume is around
-8db and in Live is around
-6db, why is that?
It’s almost certain that Live and FL have different metering algorithms for their channels and/or busses. Also the summing algorithms and panning laws are probably different.
Most probably it's due to different panning laws https://www.gearslutz.com/board/music-computers/814978-fl-circular-triangular-panning-law-other-daws-getting-clear-mixes.html
Try switching the panning law between "triangular" vs "circular" in FL Studio. https://www.image-line.com/support/flstudio_online_manual/html/songsettings_settings.htm