Hello! I’ve tried just about every note taking and knowledge management tool available for the Mac. It’s something I care about a lot. I’ll try to answer from my perspective.
Are there other apps that are just better than Notenik at doing this stuff? Has Notenik just been left in the dust, so to speak?
Your closest competitor is probably Obsidian, but trying to compete feature for feature would be a fools errand. Obsidian is nice, but it fails on being a true Mac app since it’s Electron based, and sometimes doesn’t behave in a way a Mac user would expect. Notenik hasn’t been left behind, in my opinion. It might be the only one in its class that’s a valid VoodooPad successor. Being a solo developer on a passion project is a benefit, the community of folks on the Mac that care about their apps is what makes the Mac so special.
And then, if there are certain features that Notenik lacks, what are they, and how important are they? I know some things are out of reach for me, as a solo part-time developer, such as making an iOS version of the app. But are there other features that Notenik lacks that makes it non-competitive in this space?
Some, but honestly I’m not sure how important they really are. I posted a list of questions and/or feature requests before I noticed this post. I wouldn’t worry at all about an iOS app. Notenik uses plain text files, and at least in my use case I’m only interested in maintaining and building out my professional knowledge base. After 25 years in the industry, I forget too many things and need a way to quickly remember them. Notenik, for me, answers a few questions: What happened? When did it happen? How did I do a thing? What are the steps for doing a thing? Why does this thing exist? It’s professional memory for when my memory fails me. (I can never remember the specific aws cli incantation for deploying a CloudFormation update, for example.)
Are there things I should be doing in order to attract new users? Where do you guys look for this sort of stuff? Reddit? Twitter/X? Mastodon? Medium?
The Mac Power Users forum is frequented by influential folks in the community. I’d definitely participate in the conversation over there. I wouldn’t use it as an advertising channel, (not that I think you would), but if you’d like to get more folks talking about Notenik that’s a good place to start. Most of the Mac community I’m aware of moved off of Twitter and over to either Mastodon or Bluesky.
And would you be interested in a monthly email about Notenik? Would that be helpful?
Sure! I’d love that. 
And again, thanks for making Notenik. I was this close to starting a project of my own very similar to it, I’m very glad you’ve taken this on.