Is Offline Mining Actually a Thing?

I’ve always had an eye for earning passively and amongst my strategies as everyone in my cycle, is mining fringe tokens. In the recent past, I believe a lot of miners were able to earn some substantial rewards from tokens like Avive, Ice etc…I just wanted to know how that could be feasible and how they would be syncing the data on the blockchain etc? Have anyone heard of this? How does it work? Is it worth it?