I don't know the specifics of this example project (and am honestly too lazy to replicate it on my own computer) but here is my debugging process for stuff like this:

1. You got a 404 response, which is different from the nothing-ness response you'd get from going to like localhost:12345 or some random port. This means that a web service is actually listening on port 5000, receiving your request, and serving you a 404 page; is any logging happening on the console when you access this page?
2. Are you supposed to access your app over a web browser (like it serves an HTML page) or is it a REST API that you would use a different tool to access (usually a browser extension or some CLI tool)?
3. If you're supposed to access your app over a web browser, try going to localhost:5000/index.html or something
4. None of your https endpoints will be set up by default probably, but anyway you can't listen over https (aka SSL aka TLS) without having some kind of a certificate, self-signed or otherwise; usually for local testing you set up a self-signed cert which when visited in the browser will take you to the "connection not secure" page since your browser doesn't trust random certs, only those that can be chained back to a root of trust (aka big companies like microsoft or LetsEncrypt)

emergency bump amber whataboutism

Oof I know nothing about .NET but I'll look

~~One thing you might want to try is running visual studio as admin? (taken from the readme of this github)~~ Honestly idk if this is it because:

404 error means you did reach a listening web server, just that the url doesn't exist.

Can you link that default server code?

404 means your browser was able to successfully ping your server and get a response, but there wasn't an endpoint implemented for the one you hit

Maybe it's missing a GET for the default empty endpoint