Only this specific curly braces syntax, which is less powerful than the still-supported '{$foo}' variant: https://wiki.php.net/rfc/deprecate_dollar_brace_string_inter...
Kinda odd that Bash has had this syntax since forever, Perl as well, JavaScript went out of its way to add it as well, and now php is like: let's remove this syntax specifically but allow typo variants of it!
Oh well. Not like I was using it, that is, I use the bare "$foo" syntax and try not to make string interpolation too complicated with inline expressions or some such. Just, I could have seen the logic behind switching to the more universally supported syntax and deprecating something else rather than doing their one-off thing.
I'll also point out that in shell assignment looks like
a="foo"
$a="foo"