Hi there!
Disabling downloads is officially supported for Pro and Enterprise only.
Setting the limit to -1 threw an exception in versions prior to v0.54, and while this might have worked as a workaround, this isn't the intended method, so it is not officially supported.
With the update in v0.54, the minimum for MB_DOWNLOAD_ROW_LIMIT has been raised, which means that the previous workaround won’t disable downloads anymore.
There is also the possibility of using a reverse proxy to block downloads: