1.  go to your mongodb-compass location (mine was in /lib/mongodb-compass/ otherwise find the location with which mongodb-compass)
    (Windows = 'C:\Program Files\MongoDB Compass\')
2.  in mongodb-compass/resources/ unpack app.asar like this:

    npx asar extract app.asar destination_folder

3. in destination_folder/src/app/:

    add darkreader.js and append the following function to it:

    function toggleDarkMode(){
    DarkReader.enable({
        brightness: 100,
        contrast: 90,
        sepia: 10
    });
    }

4. in the same folder, add the following line to index.html, just before the closing :

    

5. repack the app and replace the old app.asar with this one (don't forget to backup the old one in case you failed the file editing):

    npx asar pack . app.asar && cp app.asar ..

6. relaunch mongodb-compass, open the devtools console (CTRL+ALT+I) and type: toggleDarkMode();