Sharing Photos and Music with Apple TV

I have an iMac (Catalina 10.15.1) and a first generation Apple TV, also up to date.

I want to show photos that are stored on the iMac on my TV using the Apple TV device. I have family sharing turned on and media sharing also turned on. I only have the one AppleID and both devices are logged in to that account and connected to the same wireless LAN.

Yet, on the TV under "Computers' there is nothing showing - just the option to switch off Home Sharing.

Have restarted both the iMac and the Apple TV device but nothing changes.

Can anyone help please?

Thanks in advance,

Cliff, Brighton UK