Hi there, @Jacqueline_Fell and @Bastien_Siebman-
Great question here! I had to do some digging myself and it looks like the tasks with the grey arrow indicates whether the task has metadata (either a description, subtask, attachment, or comment).
Thanks for bringing this to our attention! I’ll share this with our Product Team. Maybe we can find a better way of letting customers know what this arrow means in-app.