Brilliant!
On the staging site I fixed the syntax as you suggested, disabled all the plugins, emptied the cache and it still wouldn’t save but I switched themes to twenty twenty-one and that did the trick. There were no issues when I re-enabled the plugins or theme and the new header displayed just as I wanted it to.
Knowing I could push the staging site to live if necessary I tried a shortcut and copied the saved functions.php to the live site child theme and it worked like a charm. You fixed two issues at once, thanks ever so much.