Can I make it only sync when I ask it to (manual only)?

Yes — switch the sync schedule to Manual in Settings → Scheduling, and the recurring background checks stop. Your changes still apply instantly on screen and are saved safely on this Mac; they're sent to the cloud on the next sync rather than immediately. In Manual, a sync happens only when: you press Sync now, the app starts, or a push runs (a push always syncs first — so with automatic Push on, the app keeps syncing on that schedule too).