I hope somebody associated with Roku will read this. I may, actually, need to address it with Roku Support. I own a Roku Ultra. The model is 4660RW. The software version is 12.5.5 - build 4174-46. Some apps do not include the option to be removed when you press the " * " button. AMC+ happens to be one of them. You can log out of your account on the AMC+ app; turn the Roku device off for a few minutes. Turn it back on, enter the app, and insert your login info. When you add items to "My List", exit AMC+, re-enter, and select "My List" the section will once again be blank. To me, this seems like a Roku programming error in the cache portion of the its OS where it applies to AMC+.
Roku has nothing to do with the programming of AMC+ and the vast majority of other apps. If something within the app doesn't work properly, you need to contact AMC+.
You can't remove an app if you have an active subscription through Roku, although you may be able to by using the mobile app. Keep in mind that removing an app doesn't cancel any subscription and that's why they make it hard to remove an app with an active subscription.
Roku Mobile App - Free for iOS® or Android™ | Roku
I have the same issue. Hopefully it gets fixed.