Hi,
In Laravel 10 inliner don't work at all.
After a short look at the code, I came up with what to improve to make it work with Laravel 10:
CssInlinerPlugin.php, line 99:
} elseif ($body instanceof AlternativePart || $body instanceof MixedPart) {
change to:
} elseif ($body instanceof AbstractMultipartPart) {
I haven't tested it on a larger scale (e.g. with Laravel 9), I'm posting it as a suggestion.