PlxNative

From the project's README ("Installing"):

First time installing an app outside the LG Content Store? Follow the step-by-step installation guide. It starts with a regular LG webOS TV, a computer on the same network, and a Plex account with access to your own or a shared server. No root is required.

Set up LG Developer Mode and connect with webOS Dev Manager, then choose:

• Install PlxNative directly: add only PlxNative to the TV; install future .ipk updates from your computer.
• Install Homebrew Channel first: get an app catalogue on the TV, then install PlxNative and its updates with the remote.

Already have Homebrew Channel? Find PlxNative in its catalogue and select Install. Skip the computer setup.

Developer Mode needs periodic renewal. If it expires and LG disables Developer Mode, apps installed through it are removed. Installing Homebrew Channel through Developer Mode does not remove that requirement. The guide explains how to renew the session.

For manual .ipk downloads, verify the release checksum before installing. Homebrew Channel verifies catalogue downloads for you.

Read the full instructions