As the message says. your URL is invalid. Instead of http://localhost:8080, you typed http://localhost/8080 .
But something's listening on port 80, and if it's not nginx, it might be IIS or it might be some other app. In Linux, I could easily tell what that program was using netstat, but I'm not sure if the Windows version of netstat does that.
I'd be tempted to say it's the Spring Boot app itself, except that that's not a Tomcat 404 page, which is what I'd expect Spring Boot to serve. Plus to listen on port 80, you have to have administrator privileges.
Science is the process of replacing what we "know" with what is TRUE. Politics, alas, often prefers to be the opposite.
That page looks likes it is coming from IIS (Microsoft web server). As Tim mentioned, you mistyped the URL, so the browser is connnecting to a server on port 80 (the default HTTP port) instead of port 8080.
If you do want to see which process is listen ting on a particular port, you can use the netstat command to find the PID (process ID), and then use tasklist to find the name of the executable (in my example port 8003 and PID 24028):