Who's using (or even heard of) <abbr> and <dfn> without `title`? I kinda thought that was what made them most useful, providing the full unabbreviated version for example.
That said, opening links in a new tab/window is the less-breaky approach these days, since every page that the clicks came from is a mess of infinite scroll and reactive components and all sorts of other state that gets lost by clicking to another page and trying to go back.
Target _blank keeps the title of your page on the screen and clickable.
That's before the accessibility concerns, users don't expect pop-ups anymore and find this confusing and difficult to navigate.
Also, it allows you to ensure that if you have a button that says 'download', it will actually download the file instead of having it replace the application---the principle of least surprise.
I use it when setting acronyms in small caps. Their spelling can look like screaming otherwise.
not sure about <dfn> without a title though.