I have 2910, predecessor switch to 2920 so I assume the commands are similar. You are correct that its confusing.
I'm not sure if the trap destination screen in IMC has all the parameters for setting up v3 traps compared to what the CLI has options for setting.
This may be a shortcoming on the IMC development side or there may be some specifc way to get it to work.
I gave up and just used V1 traps even though I'm using V3 for set/get. I was less worried about trap security.
You may have to get a support session with HPE if no one else here has better information.
If you figure out the cli commands you can automate this in the Service/Configuration center by sending cli commands to target switches to save yourself logging in repeatedly, if the IMC trap UI can't handle it.