PSA: Don't Upgrade to Ghost v4
TL;DR It's utter shite. Don't bother.
Privacy leaking cross-site requests you can't (properly) disable, a mail configuration that doesn't even work, post scheduling has broken, and a shitty Members/Portal system you can't disable... Yeah, no, if the Ghost developers don't address this really fucking soon, I'm going to migrate to another software as soon as possible.
Update: The Ghost developers aren't going to allow disabling the Portal, nor will they address the unpkg.com cross-site privacy leak. Therefore, it's time to move away from this software as soon as I can.
Update 2: Haven't switched away yet. I'm just a lazy bastard.