I have been hit by that as well https://phabricator.wikimedia.org/T75716 In short you cannot delete columns but can only hide them see: D9719. Quoting myself:

So https://secure.phabricator.com/T4408 complained that it was no more possible to delete columns and was fixed by adding a "deleted" status to columns. And https://secure.phabricator.com/rPa823d143b40451b827d1fdfeb980c9d3320736d1 renamed 'Delete' to 'Hide' in the interface :-]

So yeah, hide will work for me. I did not want to hide the mess under the carpet, once this bug.

So I think this task should be merged in {T4408}

And @greggrossmeier could create a new task for: "it's not possible (I believe) to set which column is the "default" one (you can only reorder it/rename it)." for which I can't see a task :-]

It is intentional that you can only reorder and rename it. Some discussion in T6469

I also need to be able to delete columns, not just hide them. I use hidden columns for various archival statuses and occasionally need to actually look at them. Unfortunately, when I turn on hidden columns I also get all the temporary/unneeded columns that I had to hide because I couldn't delete them.

Maybe a better approach would be to let you filter which columns are visible more flexibly. It sounds like all the existing use cases are arising because "hide" isn't being used to archive obsolete columns, but because it's being used to give workboards multiple states where each state has a different set of visible columns.

For example, there could be a new action like "Show/Hide Columns" which pops up a dialog letting you check each column on/off, and maybe you could save states. Then we'd rename "Hide Column" to "Archive Column" or similar.

This could also provide a workaround for personal boards if users eventually want multiple boards. Instead of truly having multiple boards, a "Designer/Chef" at a startup could have a "Design View" of their board with the "Backlog" column and all the "Design" columns, and a "Cheffery" view with the "Backlog" column and all the "Chef" columns, and effectively separate concerns without really needing multiple boards.

We are very unlikely to support deleting columns, per se, since we don't generally let users delete anything.

I still think the original request is the best solution. Creating save states or visibility filters sounds overly complicated. Why would you not want users to be able to delete columns (other than the axiom that you don't let users delete anything)?