"resolved is undefined" error with screenshotButton in shinylive

I've been asked to get a shiny app running on shinylive (in-browser running of shiny apps via webr) and I get this error image:

unless I comment out the screenshotButton call in the ui section, in which case the app works fine in the browser.

I can only guess this is because of the way browser screenshot code works, and its beyond me to debug it at this time. My main motivation for reporting it here is so if anyone searches for "shinylive resolved is undefined" they can see this and it will save them a bunch of debugging to discover the issue is with screenshotButton.