ActorComponenets can’t be blueprints. Yet.
You might try, but it will probably either crash or won’t compile at all.
If you want to assign some default items to your inventory, you will have to do it trough either actor that owns inventory component, game mode (and just assign something to all actors with inventory), or by some other means.
In your component, you can create array of
TSubclassOf<Item> DefaultItemClasses
Add items to it (if you expose it as UPROPERT, it will show in Actor defaults), and then just add item clases to it.
Then in InitializeComponent() override, you might just spawn items from this array.
you will need to add:
bWantsToInitialize, to InitializeComponent() work.
Whatever option you choose, actor which owns inventory will be needed, to access component.