Cannot add, edit, or delete donations for the 2018 year?

In my experience, double-clicking on the field you wish to edit will usually allow typing in the pop up boxes that are sometimes used to list items.

How do you create the “supporting details" boxes in TurboTax 2019?  Double-clicking doesn’t seem to work anymore, unless the box was created last year, then last year's box is opened for editing by double-clicking.

Just so I understand.  Are you amending your 2018 tax return, or are you preparing your 2019 tax return and trying to change 2018?.  If you are preparing 2019 you will not be able to change the data in 2018.