It is very common in true Kanban use to utilize "Done" sub-columns under various activity columns.  The Jira Software does not allow that.

It should not be that hard to allow creation and usage of a "Done" sub-column, for example, under "In Progress".  Currently, this requires adding a brand new column, so if there are 3 columns between "To Do" and the final "Done", each of those columns requires a duplicate "Done" columns, so we go from 5 to 8 columns.

A sub-column would simply divide the total column width.  Yes, it would of necessity shrink the cards, but info displayed on the cards could be adjusted accordingly.

It appears there was a decision made at some point to not do this, but I've never seen it explained or defended.

Please consider this.  Also, we are using Jira Server, and have no current plans to go to Jira Cloud.