When I share a HTML file, can not view it online

Sorry for the late reply.

Setting the following inside "customizables/config.php" (see this page on how to create it: https://docs.filerun.com/advanced_configuration) will allow HTML files to be shown via web links:

$config['app']['weblinks']['allow_html'] = 'sandbox';

Be careful though, as malicious FileRun users can use this for clickjacking attacks.