Getting a widgets for custom user property in the admin view

I don’t get a widget at all. I see a form with just the fields of a default user. My custom fields are ignored. When searching for the problem I find links like Custom user: how to change the admin forms? My problem is, that I’m rather new to the topic and I found various very specific workarounds for different Django versions.

So my question is how to get it working in the simplest possible way. I can probably follow the solution from the above link and create custom forms, but I would like to understand whether that’s the preferred way, whether there is a simpler solution or whether I’m completely off with my approach.