When exactly can you add Groups?

I apologize in advance if this is something previously discussed and I’m just missing.

I am trying to get a feel for when I can add to a grouped column in a table or a view. I am trying to group a table or view, then create a new group at the bottom, and begin adding new rows that are in the group. I’d like to do this both with lookups at the groups, and rows from the same table where the grouped column is a parent of sub rows in the table.

In this article there is discussion of adding groups directly, without the need to “ungroup” the table first.

However, I can’t seem to do this in certain circumstances:

  • If I am in a column in a View that is a lookup from the Master Table of that view
  • In a subtable from Layouts View

Yet another situation I am having trouble with is this:

A few times I just started typing and was able to create a new group, but other times when I do that, the newly created group “takes over” from the one that was there when I started typing, so I just swap out one group for another.

Would really be grateful for any insight here! Thanks!