The 2021 iPad Pro supports Thunderbolt3 over USB-C. Your description suggests that you have purchased an Ethernet Adapter that uses a proprietary Thunderbolt 1/2 connector - which is not directly compatible with your iPad.
Whilst daisy-chaining adapters is not necessarily recommended, if your Ethernet Adapter has TB2 connector, you might be able to connect your adapter using this:
- Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter
https://store.apple.com/uk/xc/product/MMEL2ZM/A
You would, however, be best advised to use a compatible TB3 Ethernet Adapter or Hub with your new iPad.