Probably you’d just need to make a feature request to do that if the export doesn’t have an option to remove the title bar.
Webview2 doesn’t come with much of a js api like nw.js did. It also has no command line switches. One rabbit hole you could explore are “wrapper extensions” as mentioned in the sdk manual. That would let you make a plugin in c++ land which has far less limits on what is possible. Presumably you could make a plugin that uses the winapi to get the current process, then the window, and from that change a flag to hide the title bar. Could be a pretty big time sink to figure out and do though. I won’t venture it since I just use the free version and never use exports.
Making an official feature request is probably the easiest approach.