Post the relevant excerpt of your build file. Which dependencies are you declaring, specifically, and what errors messages are you getting, specifically?
Note that android.support.design.widget.Snackbar is pre-AndroidX - is that the platform you are targeting? Any project started now should be targeting AndroidX, which uses different packages. If you're not targeting AndroidX, "implementation 'com.android.support:design:28.0.+'" would be the dependency you need (plus some other support libraries).
The Gradle marked it with red.
However it seems this particular problem has been solved. The entire project has been updated to AndroidX and I do not need to struggle with the Gradle.
I am very grateful fo help.