Does icloud photos only work with later Apple TV versions?

There have been a few changes to iCloud that may affect this.

1. My Photo Stream has been discontinued for all users.
2. Advanced Data Protection for iCloud as an account property may invalidate some iCloud services on devices with older software.

Apple TV (1st generation)

You may have a legacy device, but the real 1st generation model has had no practical use since 2018-05, so yours is probably 2nd or 3rd generation.

Identify your Apple TV model - Apple Support

Find your Apple TV model number - Apple Support

Apple hasn’t made any public statement about iCloud compatibility for legacy devices. But maybe the Apple Support staff can say something about it? Contact Apple for support and service - Apple Support