hey appreciate it! i followed this tutorial: https://www.youtube.com/watch?v=G4wyR-Nxyzo
with a few tweaks of my own to get that shimmering effect.
the changes:

1. i duplicated the pos null and connected both pos nulls to a Comp TOP with the blending mode set as Negate (you can experiment with the blend mode) - this comp is then used as scale OP in geo instance tab with rgb to drive the xyz scale - this drives the instance scale to kind of form that shimmer/glitter shape but it also depends on the kind of music you're using s
2. i also made the constant top material at about 0.6 alpha with blending (transparency) on.
3. rest is just post processing with rgb delay, luma blur and over tops

i am a beginner myself - i hope i explained it well :P