i'm having the same problem, i need to update feather but the feather site isn't letting me download it. i am able to download directly from the github site but i downloaded several of the links and none of them seemed to work. is there a specific one that needs to be selected for tails, and how do you get it to run after downloading? any help would be appreciated!
short version:
1) download the feather-<version>.AppImage file
2) move it to a folder inside persistent storage
3) right click the AppImage and select “Allow executing file as program” (or you could just run it from terminal)