wp-includes/compat.php:427Converts a string from UTF-8 to ISO-8859-1.
$utf8_textstringstring function utf8_decode( $utf8_text ): string { _deprecated_function( __FUNCTION__, '6.9.0', 'mb_convert_encoding' ); return mb_convert_encoding( $utf8_text, 'ISO-8859-1', 'UTF-8' ); }Introduced in 6.9.0. Unchanged from 6.9.7 through 7.1.0.
Signature, return type and hooks compared across 3 parsed releases.
src/wp-includes/compat.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.