Available from version 1.40.0 (Gerrit change 884482)
Replace the default signup page content about the benefits of registering an account ("Wikipedia is made by people like you...") on Special:CreateAccount.
Define function:
public static function onSpecialCreateAccountBenefits( ?string &$html, array $info, array &$options ) { ... }
Attach hook: In extension.json:
	"Hooks": {
		"SpecialCreateAccountBenefits": "MediaWiki\\Extension\\MyExtension\\Hooks::onSpecialCreateAccountBenefits"
Called from: File(s): specialpage/LoginSignupSpecialPage.php
Function(s): getPageHtml
Interface: SpecialCreateAccountBenefitsHook.php

For more information about attaching hooks, see Manual:Hooks .
For examples of extensions using this hook, see Category:SpecialCreateAccountBenefits extensions.