MacBook monitors are normally run in a scaled resolution, which uses the extra pixels of high-resolution monitors to enhance the clarity of text on the screen while keeping everything in the same size. However, this results in the screen being substantially "zoomed in" with everything much larger than it should be.
If the screen is running with its original, non-scaled resolution, you get much more space to work with, which may be good for those trying to squeeze every inch of the workspace from a smaller MacBook.
Try in the built-in controls first
Apple contains some controls to change how the zoom in the display is which you can find under the "Display" settings in System Settings:
If you are right now using the default settings, it is probably best to try this before using a third-party solution.  Drive on Native with Retina Display Menu
Retina Display Menu is a simple menu item that allows you to select a custom resolution from a drop-down menu. It is an older app but has no problem running on macOS Mojave. If it stops breaking in the future, try SwitchResX, which has been updated much more recently, but is a paid app.
Download DMG for the app from the release link at the bottom of the app's page and open it up. From the icon in the menu bar you can choose which resolution you want to run.
RDM allows you to run higher resolutions than your built-in screen, but they will be blurred as it will have to interpolate. Here my 13-inch MacBook has a built-in resolution of 2560 × 1600, but can run closer to 4K with scaling. However, it does not look very good, and it can be too little to read, so it is best to stick to your built-in resolution. You can find your built-in resolution under the "View" tab in About this computer.
RDM supports multiple monitors at the same time, and even to change refresh rates for the high-update frequency, it may be limited if you have an older DisplayPort cable.
However, it is not without any bugs and inconveniences. Even if you start the app at startup, it does not load your default resolution, so you manually select it. If you use multiple monitors, when disconnecting your secondary monitor, your MacBook screen will be reset to its default settings and you will need to re-select the resolution you are using. Sometimes it will show up and you have to choose the resolution twice. Overall, it does its job quite well.
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