[daniellumertz]

The Volume envelope needs to be already ON on the tracks or this script will fail.

function Main()
  sel_item_count = reaper.CountSelectedMediaItems( 0 )
  
      for i = 0, sel_item_count - 1 do
      
        sel_item = reaper.GetSelectedMediaItem( 0, i )
         
        sel_item_vol = reaper.GetMediaItemInfo_Value( sel_item, "D_VOL"  )--volume
        
        sel_item_time = reaper.GetMediaItemInfo_Value( sel_item, "D_POSITION"  )--time
        
        sel_track = reaper.GetMediaItemInfo_Value( sel_item, "P_TRACK"  ) -- track
        
        env_name = reaper.GetTrackEnvelopeByName( sel_track, "Volume" )
        
        reaper.InsertEnvelopePoint( env_name, sel_item_time, sel_item_vol, 1, 0, false )
        
        reaper.SetMediaItemInfo_Value( sel_item, "D_VOL", 1 ) 
      end

end

reaper.Undo_BeginBlock()
Main()
reaper.Undo_EndBlock( "Script Item Vol to Envelope", 0 )

Also I started to make scripts like this quarantine, so I may missed somethings hahaha