You can add and edit the columns of your public board at any time, but if you’re not the creator of the public board, you won’t be able to edit or add columns.
To allow users to edit and add columns to your public board, you can access the settings of your board and select the "Allow anyone to edit" feature. This article explains how this feature works. Click here to check.
If you’re the creator of a team board, you can edit and add columns at any time. Team members can also edit and add columns to your team board.