Perpetual Licenses are how most high-end software has been acquired until now. There is an initial cost to purchase a license, plus an annual support and maintenance subscription cost that entitles the owner to all updates and technical support. For example, a Perpetual License of PHPKB Enterprise (MySQL) edition with 5 admin users as of April 2022 is $665 plus a $135 per year support & maintenance subscription ($800).
One advantage of a Perpetual License is that it costs less over time. Also, if you fail to renew your Perpetual License the software will continue to work. However, there is a disadvantage if the subscription is not maintained. You will not receive any new software updates and you will not be able to upgrade to a later release.