Have you tried OSMand? I used it for navigation by foot and car, and in many cases it has equally nice public transport as gmaps. Otherwise I only use the local apps from each provider, so WienMobil and Scotty for Vienna/Austria for example, because google does not know about outages or disruptions in many cases. But that’s my experience in Europe, so your mileage may vary.
I can’t remember exactly, but I think the only problem was that you can’t (or at least I was not competent enough) add existing markdown files which are already in nextcloud to the sync process. So instead I added the empty named markdown files in obsidian, triggered the sync, and then populate each file on the desktop. And I was very picky about my folder/vault naming because of my desktop setup (and the rest of my cloud structure), but generally it is really easy to set up if you have tried it once on some dummy data so you don’t accidentally ruin something.
I do not use any"thing" apart from the aforementioned sync plugin (called ‘remotely save’), as I am very standards compliant with my stuff. But I think the editor is very extendable in comparison to other android options.
I use obsidian on my phone, with the WebDAV sync plugin to my self hosted nextcloud and vim on any pc or laptop. I would recommend to back up all existing notes as markdown files, set up the obsidian vault (it’s just a folder) as you plan to use it, and then reintroduce all content from the pc. Otherwise, there might be strange conflicts with the sync plugin.
Hope that helps
This scheme would only really improve security when using multiple different keys, as well as obviously two different algorithms. Doing the same thing over and over only grows linearly, while encryption is based on the fact that the attacker needs exponentially (not mathematically speaking) more effort to crack than was put in by the encrypting party. So if the attacker can crack it once he can also do it again with no further effort. Furthermore, most of the time the problem with encryption is not the actual cipher, but rather the key storage and distribution. Keepass for example only uses a single encryption layer (AES or ChaCha) for the database, instead offering a very robust portfolio for key derivation (basically making a big key from a small password, or translating entropy to something usable for the cipher, while keeping the determinism)
But that is essentially what two-factor authentication does. And you can also use this with fully symmetrical encryption to an extent (look up how OTP works with keepass for an example)
There is also some pretty good literature from the early days of the us military opsec, where they lay out very well the incremental steps into doing it better and better.
Hope that helps, but I am not qualified to be cited on this information :)