I’m in the same boat. Plus, the iPad app was not great at the time, which is very important to me (I read and annotate papers a lot on my iPad, it is an ideal device for this). I dug a bit to see if it was likely to be resolved soon, and it did not seem like it. So I find another solution, which in retrospect was a good thing since that was 5 years ago and the situation has not changed since.

FWIW I ended up using Bookends, which can use iCloud for hosting and synchronisation across devices. I wasn’t thrilled initially because it’s a fairly obscure app, but both the Mac and the iPad apps are great. The developer is very friendly and reactive, and it’s been rock solid for years now.