I've been working on #Esperanto lessons on Duolingo lately because I'm fascinated by its prominence and use in early international #leftist movements and want to do my best at reclaiming that in a one-person campaign. Not doing, like, great at retention, but trying all the same!
If you're having problems with retention I would recommend using Anki. Other Esperanto learning resources are available at https://kbin.social/m/learnesperanto.