Yes, you can connect your iPad to TS4’s downstream Thunderbolt port, USB-C or USB-A and use it as an external display for your Mac.
You may need to reboot your Mac and iPad if there is a timeout error.
For more information about Apple Sidecar, please visit https://support.apple.com/en-us/HT210380
Notes: All CalDigit docks and hubs can support Sidecar through Thunderbolt 4 port, USB-C and USB-A port on the dock. TS3 Plus supports Sidecar over USB-C and USB-A ports on the dock, but not downstream Thunderbolt 3 port.