I have found myself continuing to use Keep for the same reason I adopted it in the first place. It runs in the browser and it's usable everywhere without me needing to do anything.
I need to take notes on a computer at multiple different work places without taking time to install something nor asking anyone if I can, I need to also use it on my phone as well as my home machine, I need to be able to share it with others and have a reasonable chance they'll be able to see and/or edit it without needing to know or do anything themselves to make that happen and I need it synchronise everything with no intervention or administration on any machine I may use it on whether I own it or not. It sounds entitled, but also, I really don't want to pay for a glorified note pad even if something cloud based like this is inherently more expensive and complicated than that.
SyncThing would be great if I only had to worry about my own hardware on which I can install the necessary things but that's not practical when I don't know what machines I'll be using down the track and I most likely won't own them.
It's a shame because I actually really don't like Keep. I don't like it for the privacy implications (though if I also don't want to pay for what does then I don't really have a leg to stand on there), but I also hate using it. The interface is annoying, needlessly, and I can only indent one level, which for a notetaking app is infuriating. It also limits the length of a note, which fits with the spirit of a quick note taking app rather than fully fledged word processor which Google also offers but, still, having any limit at all I super annoying. I also particularly dislike the touted feature of rich previews of weblinks because it becomes hard to see where my notes end and previews begin and ironically, despite my complaints mostly being about how basic Keep is, this is too sophisticated a feature for a notes app. I'm using it to make lists of things, if I want to see the page or information on the page I've linked to in a note, I'll just go to the page.
I use Keep as a product of necessity but I don't like it. That said I found that I only started using it thinking it would help me be more organised at with and while it has helped a bit with everyday life, I eventually found that for work there were better ways of achieving the same thing, mainly with a spreadsheet, and I can do that using Google's Sheets product with the same advantages that Keep had so I've been gradually moving away from Keep anyway.
Since Obsidian just uses markdown files, I use a more lightweight app for android like markor that can read and edit the same files, sync them via syncthig and use Obsidian on pc (don't overuse extensions to keep the markdown clean)
Just tested it against the clock on my phone, with seconds turned on, it opened to my 20000 word canvas with 15 different notes in LESS than a single second.
Unless you're writing literal novels in a single files, you shouldn't have an issue.
I recommend Syncthing Fork, btw, it has a few more features.
You can set up a versioning system, there's like five different options but I don't know what all the differences are. You can set up your own custom amount of versions and set how long they are kept.
I have mine set to check for file changes, but you have a whole host of options for when it triggers. You can set it to run at intervals or just when changes happen, or when you do it manually. It uses damn near no battery life to keep on in the background for me.
It even has a conflict resolution system that let's you observe file timestamp conflicts and resolve them manually.
I'll probably sync both to and from my server. I'm currently paying for sync and it's very good but I'm sick of subscription creep and it's hard to justify the price per month for a few hundred megabytes ATM when backblaze is a fraction of the price for hundreds of gigabytes.