I have a rooted Verizon S7 Edge on 7.0 and whenever I try to do a system update, it reboots into Odin mode and does nothing. FRP lock is off and OEM unlock is enabled.
Rooted phone firmware cannot be updated as one does with unrooted device. Usually, you would need to unrooted, flash stock recovery and update or flash stock with Odin and then update followed by rooting.
There is an alternate way mentioned in this XDA post GUIDE -Easy way to update a rooted phone without losing data using FlashFire, which lets you retain your custom recovery and update using Flash Fire. In this process, apart from reducing steps your data and settings are intact