Also, I do not like my notes being shared with Apple, so I strongly prefer deploying a self-hosted solution.
What good alternatives are out there?
From a tech standpoint, it should be able to implement the backend fairly simply by having an authentication mechanism, a REST API and a key-value store. This should easily scale to whatever a handful of people in a household could put in it.
The bigger problem is probably the front end: for this to actually work well, there must be a client for MacOS, Linux, and Windows as well as iOS and potentially Android. For bonus points there would be a webinterface and CLI as well...
Has anyone made such solution?
One alternative I have thought of is to just use Signal's "Notes to self" feature. It kinda works, and there are clients for all the needed platforms. However, the limitation is that there is only one "note" in it, and the format is a stream of messages to yourself that you cannot really edit.
I haven’t enabled encryption on the notes although I think you can do that.
They're not. If you're not convinced, make sure that you have advanced data protection enabled.
Anything else with similar functionality is either paid SaaS or more than just notes, which you may or may not find appealing.
https://support.apple.com/en-gb/guide/security/sec973254c5f/...