utf8_strtolower() is deprecated. It was called from refnotes_reference_database::normalizeKeyText() in .../lib/plugins/refnotes/database.php:99 dokuwiki\Utf8\PhpString::strtolower() should be used instead!
I have changed utf8_strtolower() to strtolower() here and it worked well.
Jack Jackurm + PHP 8.1 warning:
I have changed
utf8_strtolower()
tostrtolower()
here and it worked well.