I bought the Ultra it some time ago and it has worked with Netflix and many other such channels. Recently I bought a local Amazon Prime Video subscription here in Greece, that works on my smart TV and laptop, however I cannot find the Prime Video channel in my Roku Ultra.
I try under Streaming Channels, but there is no Search Channels option listed there.
Thanks for letting us know about the issue you're experiencing.
Please be advised that you can activate any Roku Player or TV to any Roku account, however, channel availability/access will vary from region to region. Channels that are currently available in any given region are certified for the Roku devices sold in that region.
For more information, you'd want to contact any specific channel/service provider to inquire further about which Roku devices they support their channel (app) on in your current region.