I have just received an all nickel plate pound coin dated 2020. I've never seen one without the brass outer ring before but check my change site shows these were all made alongside the others. I haven't been able to find any more information such as why they were made and how many though.
The hologram works and the colour is totally consistent. It's like new, the inner ring reflects differently from the outer, but next to another is clearly nothing like it, and may be a very pale shade of brass at most, that you need to look very closely to see it. The microscopic dates around the front edge I just found exist can barely be seen but appear something is there.