How to change native Resolution on MBP 2015 running Mojave?
While you can't "change the native resolution", you can use the displaymode command line tool to change to the native resolution instead of scaled resolutions.

Download the displaymode binary from the "releases" section on github, and extract it if necessary.  Then from Terminal.app, cd to the directory the displaymode file is in and run:

./displaymode t 1920 1080


You can also run:

./displaymode d


to get a list of supported resolutions.