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It's both the EU3 template with the HOI2 shield layer.
Just make your flag in your photo editor of choice with Easy Flag Maker (EU3) style and run the action. Then just add the hoi layer on top of it. Save.
That, but you take the shield layers from the two styles and put 'em over the flags.
IMO the devs were really incompetent with these, since the flags aren't waving, and it looks unnatural.