dokuwiki\Exception\FatalException: Declaration of syntax_plugin_backlinks::handle($match, $state, $pos, Doku_Handler $handler): array must be compatible with dokuwiki\Extension\SyntaxPlugin::handle($match, $state, $pos, dokuwiki\Parsing\Handler $handler)

An unforeseen error has occured. This is most likely a bug somewhere. It might be a problem in the backlinks plugin.

More info has been written to the DokuWiki error log.