Cannot create unknown type
This error generally comes when the related activity packages are not installed in the system
Could you please provide us the below details
Is UiPath Excel.Activities Packages installed in the system? Kindly check the same in “Manage Packages”
If it not installed, install the same restart UiPath Studio and then check
If already exist , It seems DLL files related to the excel activities are corrupted.
please try uninstalling and installing the excel activities again.
Refer the below article for more details
Let me know if this is helpful