I use markor (https://f-droid.org/en/packages/net.gsantner.markor/) on android and it does everything I need. It's all a bunch of files, synchronized with syncthing, so I can use it on my desktop with any editor (maybe https://thiefmd.com/, maybe another one). No need for a server, I can use it while offline, it's lightweight to install and maintain.
I want to be able to access the same content from my laptop, phone, and tablet. I used Obsidian for a while with a convoluted setup (a Git repo with an iOS shortcut that fetched when the Obsidian app was launched), but it proved too slow and error-prone to continue using.
I want the whole stack to be open source, which is why I’m not using Obsidian Sync or an iOS Syncthing client. So while I don’t technically need web client, I don’t know of any other solution that would work for me.
I understand your concern, personally syncthing does a perfect job for me. I'm never editing from multiple devices at the same time, and by the time I switch to another device the content is synced. If not, I give it a little time and it makes me pause and use computers a little bit less, so it's not that much of a downside.
I use markor (https://f-droid.org/en/packages/net.gsantner.markor/) on android and it does everything I need. It's all a bunch of files, synchronized with syncthing, so I can use it on my desktop with any editor (maybe https://thiefmd.com/, maybe another one). No need for a server, I can use it while offline, it's lightweight to install and maintain.