For files, PHP's rename tries to rename(2), but if that fails for
whatever reason, it actually copies the file, and removes the
original.  The latter would indeed ignore extended file attributes.
I'm not sure though, whether this is the reason in your case.

I tried the test script from the command-line as the www-data user, and rename() still works correctly.

I've also corrected the PHP version; I have not tested PHP 8.0.

I added an inode check and confirmed that both rename() and 'mv' are being performed as copy-and-delete when run from apache. 'mv' preserves extended attributes when copying, but rename() does not.

Test script:

<?php
// Requires xattr:
//   pecl install xattr
// then add 'extension=xattr.so' to php.ini
// ASSUME: current directory is not /tmp
$a = tempnam('/tmp','my');
$b = basename($a);
for ($i=0; $i<2; $i++) {
  file_put_contents($a,'TestData');
  $inode_a = stat($a)['ino'];
  xattr_set($a,'owner','me');
  switch($i){
    case 0: rename($a,$b); $fn='rename'; break;
    case 1: `mv $a $b`; $fn='mv'; break;
  }
  $inode_b = stat($b)['ino'];
  $owner = xattr_get($b,'owner');
  echo "$fn ".($owner=='me'?'SUCCEEDED':'FAILED').", internal operation: ".($inode_a==$inode_b?'move':'copy')."\n";
}

> I added an inode check and confirmed that both rename() and 'mv'
> are being performed as copy-and-delete when run from apache.

Thanks for checking.  In this case this is more like a feature
request to me (and something that should be documented).

I disagree with it being a feature request.  If rename() switches to copy internally, it must still produce the same result.  If it fails to produce exactly the same result, it should be reported as an error, such as, "PHP Warning: extended attributes not moved".  Documentation would certainly help, for example, "Extended attributes may or may not stay with the new file", but unambiguous behaviour would be better.  I think it is most reasonable to expect that rename() and the system 'mv' command would behave the same.

Okay, switching back to bug than.  However, this will be hard to
implement for all possible information (e.g. NTFS streams come to
mind), and might not be possible in a fully backwards compatible
way.

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(https://www.mykplan.me/)php.net

Preserving extended attributes​​ mv silently discards extended attributes when the target file system does not support them. When you rename a file, only the first part of the name of the file is selected, not the file extension (the part after the last .).  (https://www.skywardalpine.net/)github.com

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(https://www.kmfusa.one/)php.net

It helped me on a current project, thank you!

(https://github.com/php/php-src/blob/php-8.1.0/NEWS)(https://www.mykplan.life/)