Ext HDD to Ipad connection (usb C to Lightning adaptor)

If you have updated your iPad to iPadOS13.x, then it is possible to connected external USB storage devices via Lightning.

You will need the official Apple Lightning to USB3 Camera Adapter (model A1619). Don’t be tempted to buy the slightly cheaper USB adapter from Apple - as only the stated USB3 version has an additional Lightning port with which you can connect external power. Without connection to external power many (if not most) USB storage options will not work with your iPad.

In theory, yes. However, external HDDs tend to more problematic as they draw a lot of power - plus both drive formatting and partitioning can have huge influence on compatibility.