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.
Trilium. Tried a bunch but fell in love with this one. Others either didn’t have support for inline math or weren’t wysiwyg (Joplin). Also easy syncing between computers with its own server in docker, and it even doubles as a web version of the app.