Two questions pertaining to connecting 2020 iPad pro to a powered USB hub.

USB-C and Lightning are fundamentally different - both in the physical connections and in electrical/signalling standards.

If your iPad has a USB-C port, you might as well set aside all consideration of the Apple-proprietary Lighting interface and interface converters and adapters.

If your iPad has USB-C, you can directly connect to other compatible USB devices. That said, you still need to be mindful of the need to provide adequate power to external devices that lack their own power supply - and the ability to charge your iPad whilst it being used. The simply solution to both is to use a powered USB Hub - that provides power to connected USB devices that require it whilst simultaneously providing power to the iPad.

Some USB Hubs have the older USB Type-A ports, others have USB-C. You may even find USB Hubs that feature both USB Type-A and USB-C ports.

If you need to connect your iPad to a USB Type-A port, you simply require the correct USB cable:

• mophie USB-A Cable with USB-C Connector (1 m)

https://store.apple.com/uk/xc/product/HN892ZM/A

The are many USB-C dock/hub devices from which to choose - some include 3,5mm headphone jack, wired ethernet, SD-Card readers, USB and HDMI ports etc.

Whether you choose a basic powered USB hub, or something more flexible, is entirely up to you - although for your iPad, if you choose one of the multi-function devices, you might be well advised to select one that has been demonstrated to work well with iPad. Do some research and choose wisely.

As for your older HID devices, such as keyboard and trackball, iPadOS does support standard USB keyboards - and offers basic mouse support for two/three button mouse with scroll-wheel. Anything more complex that nominally requires installation of device driver software is not supported by iPadOS.

iPadOS provides full support for Apple Magic Mouse 2, Magic Trackpad 2 and the majority of Bluetooth wireless keyboards.

If your iPad has a Lightning port - and you seek to connect a USB device to the iPad - you will require a Lightning to USB3 Camera Adapter. Don’t be fooled by its name; this adapter contains the Lightning/USB interface converter.

You cannot simply use a USB-C to Lightning cable to directly connect USB accessories to a Lightning equipped iPad. USB accessories with USB Type-B connections (or a cable with a USB Type-A connector) require connection to a host device with a USB Controller / USB Root Hub.

The required USB hardware components can be added through connection of the Apple Lightning to USB3 Camera Adapter. This adapter contains an Interface converter, USB 3.0 Controller and USB Root Hub - presenting a USB 3.0 Type-A connection to which you may connect many (but not all) categories of USB devices. USB Device support by iPad is generally limited to Mass Storage devices, basic HID devices (such as wired Keyboard and basic Mouse) and some audio.

The Lightning to USB3 Camera Adapter also includes a pass-through Lightning port - to which the iPad Power Adapter can be connected.

For iPad models that incorporate a USB-C port, you have greater flexibility in the devices that can be directly connect to the iPad - as the necessary USB Controller is already incorporated in the iPad hardware; no interface conversion is required.