To make beatmaps ( levels ) for Rhythm BOOM, you need to use Chromapper
Video tutorial:
Note:
the new version of Chromapper auto creates the explained folder structure for you when you first launch it ( you simply need to select an empty folder as the Beat Saber installation folder )
Video summary:
inside “Beat Saber_Data”, create 2 folders called exactly:
copy the path to “mychromapper” folder and paste it in Chromapper program ( as shown in video above)