This was detected as part of MDL-73587 (PHPCompatibility complete run against codebase).

Function strftime() is deprecated since PHP 8.1; Use date() or IntlDateFormatter::format() instead

We have one case in SimplePie library:

• lib/simplepie/library/SimplePie/Item.php : 882

Apparently it's not used (because tests haven't detected any problem), but surely, worth checking if a library upgrade / local patching / report upstream is needed.

Note this was fixed globally @ MDL-75100, this is just the only leftover detected that we need to verify and decide about.