gosuki is a new #localfirst open source (AGPL) bookmark manager that doesn't require a browser plugin since it simply listens for updates to your browser's bookmarks.
It looks like in order to sync across devices you need to pay once ($59) for p2p-sync functionality. There isn't mobile support, other than a routine export of bookmarks, to a folder shared with syncthing (& isn't syncthing on Android dead?)
Edit: it's not dead yet, see below.
