It's the Cross of St George of England with above the centre from the cross the protect of the normal arms of East Anglia, blue with 3 gold crowns. The arms are effectively identical to the little arms of Sweden, from where by the East Anglian royal dynasty, the Wuffingas, https://andremoqwc.blogkoo.com/the-greatest-guide-to-medieval-anglo-saxon-flag-52541066