I used to use in SMF 2.0, works fine
$body = '𝘁𝗲𝘄';
$body = $smcFunc['htmlspecialchars']($body);
$msgOptions = array(
'body' => $body,
);
createPost($msgOptions, $topicOptions, $posterOptions);
but in SMF 2.1.1 no longer works, now I returned this
𝘁𝗲𝘄
It's working as intended.
Entity 120321 is Unicode 1D601, which is a 4 byte character. The *only* way this goes into a utf8_general_ci table is in Unicode encoding.
If you manually modified your database to be utf8mb4 it won't natively be supported by SMF.
The conversion of 4-byte UTF-8 characters to entity form was introduced in 2.0.10 - I wrote the code for it. The 2.1 behaviour is not new - if it is 'new' that means you weren't encoding the data correctly before inserting it.
You're right, it was my mistake