Couldn’t get cc to activate on Prime. Found Instant Replay was on. Turned off and cc returned. But menu is missing to adjust font size, opacity etc. I verified it does show and work when using default Samsung tv Prime app. I have Roku Ultra couple months old.
Different Channels/apps behave differently depending on their coding and development.
For Amazon Prime Video, you toggle the Closed Captioned (CC) directly from Amazon Prime after a video begins to play. (Use the Down arrow on remote to toggle Overlay Info Banner and then navigate to the little speech icon/subtitle menu to select on, off, or replay).
The actual Display format of the Closed Captioning is configured through the Roku device, not the Amazon Prime app. Navigate on your Roku device to Settings/Accessibility/Captions Style to change the appearance of Subtitles and Closed Captioning.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102