To be explicit, on the Digitakt itself, you have to deliberately save it as a sound to use it as a sound, otherwise you’re just using the wav (which is what happens when you set a track sound). The sound pool is a seperate way of assigning more than one “sound” wav sample or whatever, per track (all your drum sounds on one track for example).
After you modify your sample wav (or even just load it unmodified, if you want it to be a sound that can be used in the sound pool) you need to use the import export menu to save it as a sound and add it to the sound pool. After that it’s retained in that dtsound format that can be moved to your pc via transfer as rtme said.
“Sound” is just a jargon term referring to the way it is saved and used, it’s just a term to differentiate the sound files from the samples they’re based on. But to use the word “Sound” is confusing because it’s such a general word.
Quoted from a prior thread, but this is specifically how to use it.