Just plainly and simply doesn't work at all

In the entire 7+ years of this plugin I have never seen this happen. Either you have configured it wrong, or you have something else on your site that is interfering with the plugin.

Yep i’d say you’ve done something wrong also mate!

It is very simple. Just use the source page & target url without your domain name. For eg:
Source URL: myshortcut
Target URL: myshortcutlongurl

so the when you type your url https://www.mydomain.com/myshortcut
will redirect to

https://www.mydomain.com/myshortcutlongurl