USB-C incorporates other individual standards that describe the physical and electrical interface - and an entire family of optional services that can be supported over the USB-C connection. USB-C is not a one-size-fits all. USB Power Delivery Protocol is just one of the standards that may be supported by a specific device.
For any particular hardware/standard to be usable with any USB bus, all devices in the connection chain must support the particular feature/service. Beware of manufacturer specific “proprietary” features - as these are unlikely to be standards compliant.
As for your Anker components, this USB-C hub explicitly supports USB-PD with 2018/2020/2021 models of iPad Pro and the 2020 iPad Air4:
https://www.anker.com/ca/products/variant/powerexpand-6in1-usbc-pd-ethernet-hub/A83650A1
Note that this USB-C hub supports connection of a 65W USB PD Power Adapter - with pass-through capacity of 53W. This indicates that the hub consumes 12W of power. You will also see that the Power Adapter must be connected to the USB PD port of the hub - and the iPad (the device being powered) to the pigtail USB-C connection.
Be aware that your iPad supports a maximum charge rate of 18W (i.e., 1.5A @12V / 2.0A @9V). As such, allowing for 12W to power the hub and assuming that no other USB power consumers are connected to the hub, to support the maximum charge rate of the iPad a 30W USB Power Adapter will be required.
If using a higher rated USB-PD complaint Power Adapter, allowing for the 30W potentially required for the iPad and hub, you will potentially have a 35W overhead to power other devices over USB - but individual devices may be limited by the USB port to which they are connected. USB Type-A ports are typically limited to 12W (2.4A @5V).
I hope this clarification is helpful in resolving your query.
