TikTok's "Commercial Music Library" only contains music that is licence-free and can therefore be used by brands for advertising purposes. The commercial sounds can therefore also be used for advertising purposes without the brands having to ask for the rights.

It is currently not possible to include regular releases in the commercial sounds. TikTok therefore generally recommends that users convert their account from a "Business Account" to a "Creator Account" / "Artist Account". With a "Creator Account" / "Artist Account" you have access to TikTok's PGC (Provider Generated Content) library again - and therefore also to your own sounds!

You can find more information here.