Apply Last Edited Fade Again    ⌥⇧X

I create fades using the fade tool that is enabled in the top half of the region display. Very handy. Typically I select multiple regions and apply the fade to all of them at once. This command allows me to apply the fade easily to selected regions.

Maximum fade value is 99,999 which appears to be 100 seconds. That means that the fade values are expressed in milliseconds…

Create fades in Logic Pro — Apple Support

You can fade in the beginning of audio regions, and fade out the end of audio regions (including audio Apple Loops).

Fades are only visible if you are zoomed in enough to see the waveform in the audio region. You can create a fade using either the Fade tool or the Fade In and Fade Out parameters in the Region inspector.