Currently I’m using Joplin with Syncthing-backed file system synchronization. I’m pretty pleased with it, as I do like tagging- and Markdown-based systems.
I plan to upgrade to server-based synchronization, but before doing that, however, I wanted to see what other people are using.
Edit: So far I see a slight favor towards Joplin and Logseq, but I totally didn’t expect (and appreciate) getting so many different answers.
VSCodium on the desktop, and Markor on Android. I write everything in markdown, and VSCodium is already where I spend half my time editing and writing code, so it was an easy choice. I also use Vim for quick one-offs, especially if I’m already working on a project with it.
Like others here, I also use Syncthing to keep my notes synced between home server, remote clients, and mobile devices.