I think some comment bots are nice, like the TLDR / summarization bot, reminder bot, youtube piped links, maybe one that replaces an amp link with the original? But these bots should be labeled as bots in settings so users have the option to toggle off seeing them.
I don't like having bots post posts though, I've seen some in other instances and there's not much discussion happening in the comments a lot of the time.
I use obsidian too! while it's not open source, there's so many community plugins and all your notes are stored on your computer in markdown, so you have complete control over your notes (you aren't locked in to using obsidian). I sync my notes with OneDrive, then I use the OneSync mobile app to get my notes synced onto my phone.
something similar to obsidian is logseq, it's open source but it's more geared towards bullet point notes. I used it a bit and it didn't make sense for me (I was mostly journaling, but it looks very promising if you take notes in a bullet point format!)
The most recent jerboa version doesn't work with lemmy version 17 anymore (which beehaw is on). I had the error and crash happen too. You could download a previous version off their github and it should work with v17 instances (but probably not v18).
But I'd recommend liftoff, it was recently added to the play store and it's actively being worked on! It's the app I use and I've been enjoying it so far.
I've been using flutter + android studio and I'm enjoying it (as much as you can while making a mobile app). Android studio is a lot but it includes android emulators which is nice to test stuff on if you don't feel like getting your phone.
You'll need to install flutter (works on windows, mac, and linux), android studio (I think vscode also works?), and you can download a sample project, open it, build it, and run it. It's a great way to see how it works. Then you can create your own project and go from there. Flutter has a lot of packages which I would recommend at looking through (if your app is simple you might not need any of these though).
Once you build and run the app on your android phone, it's there and you can use it. You don't need to upload it to google play or anything else (unless you want to share it).