Many creators offer free dark & moody presets in ZIP packages, usually containing XMP files for desktop or DNG files for mobile.
Download the .dng file to your phone, import it into Lightroom, open the photo, tap the three-dot menu, and select "Create Preset". Download Preset Lightroom Dark Mode zip
Download the ZIP, unzip it, and import the .xmp files by going to File > Import Profiles & Presets . Many creators offer free dark & moody presets