LG G6 should come with an app "LG Mobile Switch" that lets you transfer data from old phone to new phone. I didn't try, but it should transfer most of the transferable data, like contacts, files, SMS. Usually, apps are not transferable.
I never use these in-app transfer apps, because I want total control on data transfer and sync, to prevent garbage from loading into my new phone. For apps, many File Explorer apps support APK backup and restore. I used to use ASTRO File Manager, but nowadays I re-download.
For SMS and call logs, I recommend "SMS Backup & Restore". It has an option to transfer over Direct WiFi from one phone to another. Both devices must install the app to work.
For Whatsapp, go to Settings -> Chat -> Chat Backup, and enable Google Drive backup. If you want to include videos for backup, check the box. Then on the new phone, during new Whatsapp sign-in, it will detect backup and ask you to restore.
As I review phones very often, I do that frequently and has become second nature. The critical data that needs local data transfer is call logs, SMS, and my audio files. Everything else is stored on the cloud so I just install the app, login and data is re-sync.
And because I review phones, I like to do the entire process manually to experience and see how good or bad the new phones are.
