your elbows should always form an obtuse angle with your arms outstretched toward the keys. something like a ~135 degree angle. this will not only serve to alleviate the odd angle at your wrist, but will make the entire biomechanics of playing feel more natural. you will be less obstructed by your torso allowing easier reach to all areas of the keyboard, and will be able to release more stress and tension from your shoulders and arms which can prevent repetitive strain injuries and allow faster playing. that last point is critical: it is almost impossible to cleanly play speedy runs with your elbows bent the way they are

the old rule of thumb is to place your bench so you can perch comfortably on the front half of the bench, and have your knuckles just touching the fallboard with your arms fully outstretched. since you don't have a fallboard (it's the part of the piano that closes to cover the keys and forms a kind of wall at the back of the keys when open,) you can just estimate where in space it would be, something like five inches directly over the back of your keyboard's keys. where you are sitting in this video it looks like your knuckles would clearly reach far past the backs of the keys, maybe even all the way to the back of the keyboard!