I have already seen in some project, that in some of them is using libs and libs group: instead of implementation or deprecated compile. After local switch to implementation everything looks fine and works correctly.
Example:
libs group: 'com.google.code.gson', name: 'gson', version: '2.8.6'
instead of
implementation group: 'com.google.code.gson', name: 'gson', version: '2.8.6'
Is there any difference between them?
libs, implementation, compile are known as dependency configurations (configurations for short) in Gradle: https://docs.gradle.org/current/userguide/declaring_dependencies.html#sec:what-are-dependency-configurations
They are essentially a "bucket" to place dependency in. The Java plugin defines quite a few configurations: https://docs.gradle.org/current/userguide/java_plugin.html#sec:java_plugin_and_dependency_management
The libs configuration you mentioned is not part of any standard/provided Gradle plugin. So, it is provided/created by some other plugin you have applied to your project. Or you have defined the configuration yourself in your project somewhere.
The implementation configuration, provided by the Java plugin, are for implementation details of your application or library. In other words, these are "private" to your application/library and will not be available to consumers' classpath.