I have same (or just similar?) problem on Windows.
I switch between Obsidian 0.9.17 and other apps frequently, taking notes in Obsidian in Edit mode. After each switch, I have to click in the edit pane, to be able to start writing again, as cursor/focus is lost.
Not sure if it could be an Electron bug (or perhaps Electron on Mac only) - I have used other note taking apps (at least 2) based on Electron on Windows, before switching to Obsidian, and don’t remember experiencing that issue there.