There is no license (free or paid) for Rider for Unreal going forward. Rider for Unreal was strictly an early access/preview build.
But, the Unreal support has been rolled into the full version of Rider so if you buy a license for that it includes the features you’re used to from Rider for Unreal. It’s one year license so you have to keep ponying up, but there are details for a perpetual/fallback license after you been paying for 1 year. It’s a little convoluted honestly, so you should checkout their own explanation of it.