This extension will not compile against PHP 8 unless the following patch is applied: http://www.fedtrek.com/staff/omega13a/rpms/fc35/php-pecl-gender-8-compadibility.patch
(I would submit this to the appropriate bug tracker but I can't find it. Clicking on "Report New Bug" on the Pecl Page takes you to a page saying the bug tracker no longer accepts non-security issues and there isn't any alternate place aviable)