Well I'm not really surprised - Installing System Apps with an apk usually doesn't work - If you're really bound & determined to install the apk - You would have to Clone it with an app designed for this - Probably not worth the trouble in my opinion... If on the other hand you wanted to install Android Messages that would be simple 😉🐧
I am sorry but it doesn't work. Latest Samsung Messages app is for Android Pie or less!!! But you can try with the Messages app of the Galaxy S9 ( the one with the blue icon). It was released for Android Oreo and I am sure you got Oreo on your S7. So if you have root on your device you can change the Messages app with a File Explorer with Root!!! Looking forward it work for you!!!
Yes if you have a device that CAN be Rooted (which the S7 is able to be Rooted) Then you can uninstall (not just disable) any System Apps & Then you would be able to install a new version of the system app - Important to note that just because you could install an app that is designed to only work on Pie or higher - ie: Android Q doesn't mean that it will work on an unsupported OS 😉
