I would like to add one simple issue and solution I have not found one the web.
If the "remote" is a new machine or a newly formatted machine - ensure that you have logged on to it using your username and password at least once before trying to RDP into it. From what can gather, Windows caches something on the "remote" when you log in once. After that your credentials work from the machine you are RDP-ing from. Since Windows 11 Pro allows/sets the option to only allow local logins with Windows Hello, in my case with a new Windows laptop I had never logged into the machine with my password. Once I realized that, it was easy.