You might like Blinko. It seems similar to Keep to me. I set it up for awhile, but it didn’t give me anything beyond what I already have with Joplin, so couldn’t justify keeping it or transitioning to it. Here’s a video from DB Tech on the set up process: Self-host Blinko with docker
Development is pretty rapid too. I didn’t track the features on the updates, but new versions were getting pushed regularly. No mobile app which was kind of a bummer, but the progressive web app integration was pretty good. It felt like a mobile app.
Edit: I forgot to mention the note sharing function, it shares a URL of the note that allows the recipient to view and edit the note through the URL. It was a little janky when compared with sharing a note between two users using themselves app, but it still worked pretty decently.