To enable VT100 (or any other emulation mose such as Linux) you must configure the terminal emulation type in the session properties.
While a terminal session is open, select "Session > Session Properties" from the main menu.
Next, on the Terminal tab, select the Emulation Type and the Report Terminal Type to Host settings.
Press OK to commit the changes.
Now, you may need to disconnect and reconnect to the host device/server toallow the client and server to properly negotiate the emulation protocol.
This setting is saved in your terminal session profile, so that when you open the session again, this emulation type is remembered.