It's the very opposite. 5.40 is when it became "a stable language feature". From perl5400delta,

try/catch feature is no longer experimental

Prior to this release, the try/catch feature for handling errors was considered experimental. Introduced in Perl version 5.34.0, this is now considered a stable language feature and its use no longer prints a warning. It still must be enabled with the 'try' feature.

See "Try Catch Exception Handling" in perlsyn.