I was having the same issue and found out that My Flow does the almost the same as sync/login. I mostly wanted to sync my tabs, so just updated my sync settings on my account and enabled My Flow on the desktop and mobile apps, then added a new device scanning the QR with my phone and my tabs synced on both devices. Unfortunately, this didn’t pick up bookmarks or passwords, which I am still trying to figure out.
It’s awful as UX but I guess it’s a workaround… I just share through the Flow chat thing whatever I might need.