Doesn't seem like TP Link will be responding... The easiest way is to connect it to your router and check your router wifi status page. There's typically a few MACs on devices like these depending on whether it's running in station mode or AP mode so it's best to check it live.

BTW, if your plan is to use MAC filtering to protect your router/network it's probably more trouble than it's worth. Most wifi devices built in the last decade allow the MAC to be customized so any hacker with skill is going to break in anyway. Using WPA2 with a good password should be sufficient to block anyone without that skill.

MAC addresses have always been visible under "device settings" (for each device) in Kasa

hey have their own mac addresses. it is written on the side of some bulbs.