What should be disabled to run on an internal network with no access to the Internet?

I am setting up a site on an airgapped (no connection to the Internet) internal network. It is quite slow in loading pages. I have already added define('WP_HTTP_BLOCK_EXTERNAL', true); and define('AUTOMATIC_UPDATER_DISABLED', true)' in my wp-config.php file. WordPress still appears to be trying to reach gravatar.com and fonts.googleapis.com.

Is there something else that I need to disable in order to run WordPress without Internet access?

After more fruitless searching, I stumbled across this article from WP Tavern which mentioned a plugin then called “WP Local Dev Environment,” now called Airplane Mode. The plugin blocks a long list of things that WordPress does which require checking something from the Internet.

While it is intended to be toggled on or off depending on whether you have a connection, I can use it in perpetual “on” mode on my internal network sites. After enabling, pages that were taking 15-30 seconds to load now load almost instantaneously. BRILLIANT!