The G6 is LG's flagship smartphone for 2017. Despite this, it is yet to be officially updated to the latest version of Android. A Redditor claims to have found a beta for this very upgrade - albeit for just 1 region-specific variant of the phone.
https://www.notebookcheck.net/Android-Pie-for-the-LG-G6-European-variant-allegedly-surfaces-in-leaked-beta-form.427574.0.html