After updating to MediaWiki 1.38, I see the following message at the top of pages which include a Drawio diagram:
Deprecated: Use of ParserOutput::addModules with non-array argument was deprecated in MediaWiki 1.38. [Called from MediaWiki\Extension\DrawioEditor\DrawioEditor::parse in /var/www/html/extensions/DrawioEditor/src/DrawioEditor.php at line 281]