A: Yes. You can flash the stock Oreo KDZ file using LG UP tool.
Short, useful guide: can an LG G5 be updated to Android 10? lg g5 update to android 10 upd
A: Nowhere. It never existed. Any site offering one is fake. A: Yes
: You must have a tool like TWRP Recovery installed on the device. Installation Overview : lg g5 update to android 10 upd
: Transfer the ROM and GApps zip files to your phone's storage.
Several custom ROMs based on Android 10 are available for the LG G5, including: