Which adapter do I buy to connect my iPhone pro to my smart tv?

https://www.apple.com/shop/product/MD826AM/A/lightning-digital-av-adapter?fnode=97&fs=f%3Dadapter%26fh%3D458e%252B45b0

the fact that your tv is a "smart" tv has no barring though it works the same with all tv's or monitors with hdmi imput

Read your instruction booklet first to find out which adapter or call the toll free telephone number and ask for technical help.