Looks like you are running openHAB version 2.3 and that doesn’t include the new modbus binding. Only 2.4 snapshot builds does. Check out this link and see if you can install the 2.4 binding. One possibility is to switch your openHAB to 2.4 snaptshot. This way the new modbus binding would be available through PaperUI
For getting detailed info of your openHAB installation e.g. installed bindings and versions see this section of the docs about karaf console: