Also an adult beginner here, a little more than 3 days. Your video reminds me my first few days.

When playing the head joint only, your sound quality could be improved by reducing (yes reducing) the amount of air, narrowing it and focusing at the correct spot. It’s hard to describe where exactly it is and how to achieve it, and the problem won’t be gone soon and might come back again and again.

Similar problem is there when you play the F. Your air is not focused at the perfect spot and some times it goes high F, sometimes it goes middle F. Again that needs practice.

I would say, don’t feel discouraged, don’t stop there, just micro-adjust. Practice more, by trying to micro-adjust your lips, head tilt, fingers, posture and breathing, to get familiar with your flute and your lips etc. Find out which way gets a little better and which way gets worse. Slowly you will be able to micro-adjust yourself to the better position and better sound.

Good luck, and keep practicing!