Lost my glasses last night so not sure what am reading let alone what I type. That dog pic, if you pout the flash behind the head you’d get a nice rim light effect, yep know that is not what you are trying for. For flear and old uv filter with some Vaseline smeared on it filter will not come clean after hence OLD
That's when I've usually gotten flare, in the evening when the light hits the lens at the right time and the right angle (or wrong if you don't want flare). The photo in the OP doesn't look like flare, more like glare; it makes me want to squint. Too much looking directly at the light rather than having it bouncing off the lens at an angle.
When you find a lens that flares the way you want, you should keep it. You are correct when you say that most modern lenses are coated so well that lens flare is difficult to produce.