All templates for Joomla 3 are available for free and can be downloaded from the "Download" section.
Joomla Monster templates are working with Joomla 3.x only.
Joomla 3 support ended in August 2023. After that date and without the official support of this CMS version, you are using the Joomla-Monster templates at your own risk.
If you are looking for Joomla 4.x quickstart websites, browse them here.