Why does the resolution not change when I enable Picture by Picture on my monitor?

A monitor's hardware Picture by Picture mode does not always tell macOS that each input now occupies a smaller part of the panel. If the display continues advertising the same modes, you may need to select a suitable resolution yourself.

Hardware Picture by Picture shows images from multiple physical inputs in separate regions of one panel. Some monitors reconnect with different EDID information when Picture by Picture is enabled. Others advertise full-panel and split-panel modes together, leaving macOS without a distinct mode-change signal. The behavior depends on the monitor.

Choose a resolution for each input

Enable the intended Picture by Picture layout on the monitor, then inspect the resolution choices for each connected input. Use a timing the monitor supports for that section of the panel. For example, dividing a 3840 × 2160 panel into equal left and right halves gives each input a 1920 × 2160 area. That arithmetic does not prove the monitor accepts that input timing.

If a suitable connection timing exists but the scaling choices use the wrong proportions, review Edit native panel pixel resolution in System Configuration and Flexible Scaling. It affects scaling calculations. It does not create an unsupported physical timing. Keep a record of the original configuration before changing it.

For the underlying rendering method, see what flexible scaling and custom resolutions change.

A prepared custom EDID can expose the appropriate supported timing on compatible connections. This is an advanced workaround, not a universal Picture by Picture preset. An override that suits a split-panel layout may not suit the monitor's full-panel mode, and indistinguishable display identities can complicate applying separate settings to identical monitors.

Switch the monitor’s layout

To switch the monitor's Picture by Picture feature from BetterDisplay, the monitor must accept the relevant DDC command. If you have verified its command and values for that exact model, you can assign a custom DDC feature. Do not assume another monitor's code or on/off values apply. A command that changes the monitor's layout does not by itself select the matching macOS resolution.

For a software alternative, separate virtual desktops can be shown in Picture in Picture windows side by side. Those windows remain presentations on an underlying desktop and need their own placement and interaction setup. They do not turn the physical monitor into independent hardware inputs. See virtual screens, mirroring and streaming.

Check each input separately: the same split-panel size may be available over DisplayPort but missing over HDMI on a particular monitor. If a size is absent, compare another supported input and cable while keeping the monitor’s PBP layout the same. A successful comparison identifies a usable path for that setup. It does not establish that DisplayPort always supports more modes or that a native-resolution override can supply the missing timing.