No public method exists to downgrade ARB on post-2018 LG phones without JTAG or engineering tools. If you are stuck on a high ARB with no newer KDZ (rare, but happens for discontinued models), you cannot flash any KDZ anymore.

For many LG users, this error appears as a pop-up window just when you think the flashing process is about to begin. The message usually reads: "Error: 0x5319, CrossDL [Device Model] to [Target Model]."