Freesound Forums

If GarageBand samples/loops can be extracted/isolated from your audio work in full or in part, the result is not fully yours to relicense, burdened by Apple's restrictions, that are incompatible with any license available on Freesound.

G. GarageBand Digital Materials.
Title and intellectual property rights in and to any content displayed by or accessed through the Apple Software belong to the respective content owner. Such content may be protected by copyright or other intellectual property laws and treaties and may be subject to terms of use of the third party providing such content. Except as otherwise provided in this License, this License does not grant you any rights to use such content nor does it guarantee that such content will continue to be available to you. Except as otherwise provided in this License or in the Apple Software, you may use the Apple and third party content, including individual samples, sound sets, audio loops, photographs, images, graphics, artwork, audio, video or similar assets (“Digital Materials”), contained in or otherwise included with the Apple Software, on a royalty-free basis, to create your own original soundtracks for your video and audio projects. You may broadcast and/or distribute your own soundtracks that were created using the Digital Materials. However, Digital Materials may not be commercially or otherwise distributed on a standalone basis, nor may they be repackaged in whole or in part as audio samples, sound libraries, sound effects or music beds. You may not use, extract or distribute, commercially or otherwise, on a standalone basis, any Digital Materials contained within or provided as a part of the Apple Software, or otherwise use the Digital Materials outside the context of its intended use as part of the Apple Software. Artist Lessons are provided for personal music lessons only and may not be used for any other reason. Artist Lessons may not be commercially or otherwise distributed in whole or in part, in any format or by any means. Skill levels for Artist Lessons (beginner, medium and advanced) and descriptions are provided for convenience, and you acknowledge and agree that Apple does not guarantee their accuracy. The Learn to Play feature, including Artist Lessons, requires musical instruments.

— Apple TOS PDF

All licenses on Freesound allow other to sample your sound (= extract bits and pieces from it). Adding restrictions is not permitted by the licenses.

If an Apple sample or loop can be extracted/isolated from your track, can't be properly CC0/CC-BY/CC-BY-NC licensed.

One might debate that the samples may only be used for music but not for single sound effects, since the license only mentions "soundtracks" as permitted items.

This is similar to Cymatics.fm, though not as bad as Soundtrap or WA Productions.