I’m not seeing anything in the accessibility settings on the iOS Twitter app that allow links to open in reader view
I have this feature enabled and know for a fact that it works. The setting is indeed in the Twitter app’s Accessibility settings as depicted in my screenshot.
View attachment 121204
Are you using the latest version of the Twitter app? My Accessibility settings stop at the Video Autoplay options, nothing below that.
You might try deleting the app, then reinstall it. Try first deleting it in settings> General > Usage > Manage storage. This way you shouldn't have to log back in. If it doesn't work, delete the app on the home screen by tapping the X, then reinstall. You'll need to log in this way.