The app’s script did not run, so there is nothing to show.
To start the app, double-click
Start DMMA.cmd in the project folder, and
keep the window it opens. It builds the app, runs it on this
computer and opens it in your browser.
From a terminal in the project folder, npm run dev also
works — open the address it prints.
Why you are seeing this: an index.html was opened
straight from the folder. Browsers block the app’s script on
such pages (Firefox’s console says “CORS request not
http”), so DMMA has to come from a small local web server
— that is what Start DMMA.cmd runs. If DMMA is
already running, this page switches to it by itself. If you see this
on a website instead, the script failed to load there and the browser
console (F12) says why.