Success Uninstalling Shadow Services
I have a Samsung S8 and was facing the same issue when I searched for "Uninstall Dual Messenger" and found this thread. I resolved the issue and decided to return here and say what I did to get them all uninstalled. I didn't have a "Secure Folder" also, I already opened the "Dual Messenger" setting and disabled the available options. The missing step for me was to go to Apps > ANT+ and click Force Stop and Disable. I had already uninstalled "Copy Of Messenger" when I discovered that it doesn't remove the copy of play services and everything else. Removing the ANT+ App removed about five or six "Copy Of.." Apps as well. I hope this is enlightening. After removing all of your Dual Apps, Copy Of.. Apps & Secure Folder, Remove the ANT+ App. On Galaxy S8 With The Latest Updates As Of 6/9/20 I alas successfully removed the remnant shadow service copies that were associated with Dual Messenger.