PHP compare 2 different arrays by a value and find differences

Solution:

You're adding every record to your$recordsToDelete array because any time thebrandId values don't match, you add the record and, since thebrandId values don't match for all records, that means that condition is always true at least once for every record. Instead, compare all thebrandId values from the front end for each back end record and only add the record to$recordsToDelete if it doesn't match any otherbrandId value. For example:

$recordsToDelete = array();
foreach ($fromBackend as $backendItem) {
    foreach ($fromFrontEnd as $frontendItem) {
        if ($frontendItem->brandId == $backendItem['BrandID']) break;
    }
    if ($frontendItem->brandId != $backendItem['BrandID']) $recordsToDelete[] = $backendItem['record'];
}
print_r($recordsToDelete);
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Output (for your sample data):

Array
(
    [0] => 114466
)
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Demo on 3v4l.org

If$fromFrontEnd could be empty the above code will raise an undefined variable error. You can work around that by checking it using the null coalescing operator e.g.

if (($frontendItem->brandId ?? -1) != $backendItem['BrandID']) $recordsToDelete[] = $backendItem['record'];
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or by using an explicitfound flag:

foreach ($fromBackend as $backendItem) {
    $found = false;
    foreach ($fromFrontEnd as $frontendItem) {
        if ($frontendItem->brandId == $backendItem['BrandID']) {
            $found = true;
            break;
        }
    }
    if (!$found) $recordsToDelete[] = $backendItem['record'];
}
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although it would probably be simpler to just not execute the outerforeach loop unless!empty($fromFrontEnd);

Demo of above 2 solutions on 3v4l.org