This also affects current version (v 14) and earlier.

If a job has an error, the text of the error appears in the Additional Info column in the Jobs/Run Details tab. However, the text is truncated and there is no ellipsis button or other function to display the entire text. Please make the message accessible, as it often contains crucial information about the job failure.

I agree on this, it would be nice to be able to see the full error text. Double-click to open a text editor with the full text (like in the status bar in the sql or program window) would be usefull, or an ellipsis button as jlcox suggests.
In general, when showing data in grid views, it would be nice to have this option to see the full data, e.g. also in the table editor (e.g. comments in tab page Columns, columns and referencing columns in tab page Keys, condition in tab page Checks etc.)

A work-around is to mark the row in question and copy-paste it into an editor.

We'll check it out.