1. Opus Quad from what i read only works via ethernet to lighting adapters, not sure if it works USB-C.
2. sounds like you did not convert the library to Library "plus" so the opus cannot read the database, its just looking at the folders on your flash drive. Read the FAQ here to learn how to
https://rekordbox.com/en/support/faq/devicelibraryplus-6/
In EXPORT mode, click [Preferences] > [DJ System], and [Device Library] to configure the following settings.
- If using OPUS-QUAD as well as CDJ/XDJ
Select [Device Library Plus (OPUS-QUAD ONLY)] and [Device Library].
- If using only OPUS-QUAD (when DJ equipment other than OPUS-QUAD is not used)
Select [Device Library Plus (OPUS-QUAD ONLY)].
Unselect [Device Library].