Lumetri causes pixelation (macOS)

That media is "thin" as far as total bits and data available. Partly due to the mode used for capturing and partly due to the compression as Ann notes. So you may have to be very "gentle" with any color correction to avoid pixelation and macro-blocks.

For example, to lift shadows, do a small amount with the Shadow tool in the Basic tab, a touch of the Shadows Luma slider in the Color Wheels tab. They use different math, and splitting the process into two slightly different steps will get more correction before pixelation/macro-blocking.

And there a limits simply to what you can do.

Also ... some times using a small amount of say Neat video noise reduction plugin after the color correction can help a little bit.

Neil

Rendering as in making preview files or exporting?

We are not clairvoyant in how you used Lumetri and what exactly you are experiencing.

Post screenshots.

BTW gopro and dji footage is not great source footage to begin with: highly compressed.