I'm super new to Lemmy, does anyone who's familiar with it and Jerboa know what this is trying to tell me?
A new version of the Lemmy server software was released recently, version 0.18. It appears that the Jerboa app is now expecting servers to be on that new version. It looks like you're connecting to the lemmy.world server, which has not upgraded yet. They are waiting for a feature that won't be ready until 0.18.1
Unfortunately, there's not a lot you can do to fix this yourself - it's up to the people administrating lemmy.world to upgrade their server when they're ready.
IMO, Jerboa should not have locked out old versions so quickly.
Captcha support, which is in 0.17 but was dropped from 0.18. It’ll be added back to 0.181, which is what lemmy.world admins are waiting for.
I believe it was dropped because the 0.18 release removed websockets, since that doesn’t scale up to lots of users very well. The developers priority was understandably getting lemmy stable despite massive user growth. Unfortunately without captchas, open sign up instances like lemmy.world will be overrun by bots.