Pretty Sure This Option Hits All Your Desired Features
AnyType offers end to end encryption by default, as well as a Web3 style user authentication system where you are given backup keys to your notes instead of the usual login that has the traditional means of user accounts being hacked (but require the user have a secure place to store the key of course and the ability to find where that is later, of course). It offers a free remote backup and they are located in Germany, which if you believe privacy laws really are anything but hot air you may appreciate.
Basically it works like Notion but has a very rudimentary graphing view allowing you to visualize how you relate knowledge contained within various types of notes together, but not to the same level or distraction potential of miro. From my admittedly limited trial of it, it did all of what I think Notion is good for without the performance lags and awful navigation nightmares that Notion has always been and why I have a lot more knowledge about note-taking software then I ever wanted to have.
While only demoing it shortly, I found the template and "types" system it uses to be interesting and for those who use these sorts of apps as a complete solution to their personal knowledge base needs it would save numerous hours or the frustration of creating a template to be reused on Notion that you end up forgetting to copy when you go to use it. The blend of knowledge structuring paradigms, be it a hierarchy, zettlekasten tags or whatever else, it seemed it would work fine on this particular application and the free tier limit for storage remotely seems reasonable (they market the pro tiers mostly to enterprise it seems, but even at that grade they were a bit cheaper than other options on that front if memory serves, I am not going to research that at the moment sorry). The graph and relations thing would take getting used to, but seems worth while and the tutorials were actually decent and thorough enough in introducing the argot of the application that is uncharacteristic of most software.
Less Enthusiastic About But Fits the Bill, Probably Already Mentioned
Joplin is the other option I have used but it can have some issues with uploading and syncing that caused me to loose a bunch of notes (luckily I have other backups as well not connected to these craptastic applications for anything that's of any actual importance). The developers are dickwads, the sync has been critically flawed and the features are far more minimal, but for some it will be perfect as they need not structure their notes as extensively as others may prefer (Joplin allows notebooks, within which the structure is a heirarchy which I prefer myself to zettlekasten styles or graph based systems personally but to each their own).
What frustrated me most in using this application, which I once used to keep various things in a place I could easily copy-paste them when needed but wasn't sitting in the open without encryption for the first penetration of the server to spill the contents, was (at least at the time, this might have changed) it was somewhat obtuse to export the markdown files for local storage purposes outside of the encryption (so I could use my own key for encryption and drop them on the cloud storage solution I used then) and often it would spit out the files, but using that awful string of nonsense that the markdown files were named by the application's internal database (a potential vulnerability in design and additional attack surface).
Yet I am Not Migrating My Notes Because I Came Up With a Better Solution
It's More Secure, More Flexible and More Minimal
Instead of relying on a third party group of developers, some of the laziest people on the planet (I say as one), I figured out an acceptable solution for knowledge base management that actually works better for me, is way more secure cutting out other parties, is more flexible and is super minimal. I keep my notes written in Markdown files, either in the directory of the project they relate to or in their own directory if they relate to something less specific or more topical in concern (for example, I keep "notebook" directories for notes relating to AI, computer science in general, my study of Sanskrit scriptures as my super dry & super nerdy hobby, etc). I then back everything up on GitHub, the ones I don't mind being seen by others (even private repos are accessible to the right malicious actor). Notes I want encrypted, I keep backed up to a local-only NAS server and use my own keys to encrypt/decrypt them as needed. That way the notes are free to be structured as I want, I can rest assured they are safe and not vendor-locked, I have shell scripts that automate various aspects of them, don't have to write in org-mode (or even touch emacs with that horrid lisp configuration) and don't have to worry about them being used by abusive advertisers that have AI scan them to better market crap I don't need nor would buy anyway (not to mention government actors and other malicious third parties that want a window into my mind for whatever reason)
The only downside being not having things like columns of text, images rendered once entered (I don't preview Markdown while working on it, seems redundant since I know what the markup means right away) or any of those type of HTML5 features unless I render the notes into a mdbook style website, which I almost never do. But for the simplicity of managing the notes themselves and peace of mind I won't loose countless hours of obsessively detailed note taking, it is more than worth it for my purposes.
Thomas Leon Highbaugh