I have tried to change the sound from item pickup to chorus flower block but it didn't work. Did I do it wrong, or is it not possible at all in the current version?

Sorry, I'm cringing a bit reading the code I wrote more than 5 years ago...

In your config.yml, if you write:

sound:
  type: "BLOCK_CHORUS_FLOWER_GROW"

Does it work?

I think you can use the sounds listed in https://www.digminecraft.com/lists/sound_list_pc.php by replacing the dots with underscores.

I have already tried that and it didn't work.

I also tried removing the underscore but still nothing. :(

sound:
 volume: 1
 type: BLOCK_CHORUSFLOWER_GROW

Then sorry, maybe the API changed since? Or there's a bug in the code. I haven't touched this project in a long time, I'm not really maintaining it anymore.