Duncan has mentioned the Byzantine one a few times as his inspiration to start his first series, the History of Rome, which is awesome too. I'm sure I'll get to it eventually.
The one Duncan mentions is not the one I'm talking about, though that one is supposedly really good. The one I meant is Robin Pierson's History of Byzantium, found here:
https://thehistoryofbyzantium.com/Robin picks up immediately where Mike Duncan's History of Rome left off, with Emperor Zeno dealing with the consequences of the end of the Western half of the empire, and goes on from there. His style is initially pretty closely aping Duncan's style but he develops his own voice as the show goes forward.
Currently, his show is in the middle of the so-called Macedonian Renaissance (the late 9th through early 11th centuries), during which the Byzantines rebound pretty thoroughly from second-rate has-been power to full-on great power status again and regain quite a bit of their former wealth and power...but he's only a few decades removed from that all coming crashing down with the invasion of the Seljuks and Byzantine power reaching its lowest ebb yet.