Check out A New Plural for “Medium” by rogersgeorge. Here is an excerpt:
I mentioned this last December (2019) and also back in 2016, but it bears repeating, I suppose. The “correct” plural of “medium” is “media.”
But I’m seeing “mediums” more and more; at least when referring to something besides radio and television broadcasting. To wit:
As well as testing…
The full article is available here.