I found the way to use R128 LUFS -23, plugin with FCPX.
I think it is many with me that tried different R128 LUFS -23, plugins , as tonboster, PPmulator3, etc. and it worked in ONE way only messuring 0dB level.
If you tried to change level it stills messur the ZERO dB level. Boolucks.
But if you right click the clip and chose "Expand Audio Components", :-) none Boolucks. (you have to do it on both video- and audio träcks)