Or a hacksaw blade or a file or whatever it takes to get the head off. Then the fin should come off. However if for some reason it won’t because the screw is to long then you will need to get the drill out and drill until the screw is short enough to get the fin over it. Then slide the what’s left of the screw and plate out and dispose of it in the trash.
We had/have in orthopedics...a screw removal set(Xtract-all) and funny you mention this..i saw one at Home Depot the other day..
It allows you drill i to the screw head and back it
All in the same motion...
Given the type of screw and its condition, the Dremel tool is probably the best option. To do a good job of "drilling", the rake of the fin needs to be out-of-the-way. Or, perhaps there is enough of the screw stiking up to be able to get some vise-grips on it?