Apple TV 4K not playing Home Movies from iMac after software update

Apple TV 4K

I previously had an Apple TV unit which was nicely working but for some reason stopped working. Its primary job was to play movies I have placed in Home Movies on my iMac. As I said this was working fine since around 2012, I got a new iMac last Christmas and it has continued to work until recently.

I decided to purchase an Apple TV 4K as I thought the older one had 'had it'. Movies just would not load and I got the spinning wheel of death. I could, however, see the thumbnail and select these so I am guessing it must be seeing something on the iMac.

I am seeing exactly the same thing with the new one, I now have just 11 movies in my Home Movies on my iMac, amazingly two of these play. The others I get a There's a problem loading this content.

I've updated the software on the Apple TV 4K, reset the router, tried wifi and ethernet.

Any ideas what to do here as its driving me totally nuts.

One thing of note, is that I recently updated the iMac to Tahoe, not sure if this is when the problems started. I am running the movies from a separate hard drive and have been playing around with libraries etc. When this was working previously I just copied movies into the actual Apple TV app/interface not the iMac.

Help please

[Re-Titled by Moderator]

Original Title: Apple TV 4