I had the same exact problem...I got the "missing plug-in" message too when I tried to play an Amazon Prime movie on my 2009 Imac with Safari Version 11.1.2 and El Capitan 10.11.6...So my solution was to drop Safari Browser and go to Google Chrome (Version 88.0.4324.192) and I got immediate access to the Amazon Prime movie (Minari)...I enjoyed this great movie on my 24 inch Imac screen March 4, 2021...hope this helps...James, Columbus, OH

I had the same exact problem... I got the "missing plug-in" message too when I tried to play an Amazon Prime movie on my 2009 Imac with Safari Version 11.1.2 and El Capitan 10.11.6.

My solution was to drop Safari Browser and go to Google Chrome (Version 88.0.4324.192) and I got immediate access to the Amazon Prime movie (Minari). I enjoyed this great movie on my 24 inch iMac screen.