No, all Soundbox Instruments are compatible with both the desktop and iPadOS free versions of Soundbox Player.
If you own any Soundbox Instrument either from Audiomodern, or from any other developer you can load it into the iPadOS version of Soundbox Player.
All features in Soundbox Player for iPad are unlocked and functional, except for the Mapping & Sample Editor.
The Editor can be unlocked by making any In-App Purchase of a Soundbox Instrument on the App Store.