Oh happy day... When Soundtrap loops got royalty free! No seriously, they have ALWAYS been a 100% free. Feel free to use them in your songs as much as you like.
However - it's not allowed to take an individual loop and share/distribute it without adding your own music to it. Individual/solo audio loops 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 effects or music beds. A music bed is like if you take one of the loops, add a melody on top of it, and then sell this as a "new" loop itself to someone else.
Now go make that hit song, tiger!