Using Internet Sharing but then cannot access video/music library through iTunes to AppleTV

Thank you for that tip, but I am not trying to Media Share from the 2011 MM to the 2020 MM; I am trying to get iTunes on the 2011 MM to stream to my 4K AppleTV, as it did in the past before I purchased the 2020 MM.

The answer was right in front of me; Turn on BOTH Ethernet and WiFi in Networking on the 2011 MM and the 2011 MM will link both subnets together and now I can File Share with high speeds and once again stream my iTunes library from my 2011 MM to my AppleTV:

OS X High Sierra, which is what I use in my 2011 MM does not appear to offer Media Sharing.

I have Home Sharing turned ON in iTunes, where apparently this historic setting was located back then.

Monterey, which I use in my 2020 MM does have the Media Sharing setting you are referring to, but my home video and audio library are located in and/or connected by USB to my 2011 MM, which again is using High Sierra, and is now available 24/7 as a headless server. I keep iTunes active on the 2011 MM so that I can always now access it from my 4K AppleTV.

There are no active home video and audio files located on my 2020 MM.

Thank you, I'll try that, but I do not think that is the problem because neither computer nor the AppleTV are connected to the Router directly by ethernet; both use WiFi:

AppleTV = WiFi

Mac Mini 2020 = WiFi

Mac mini 2011 = ethernet connection to Mac Mini 2020, which has Internet Sharing turned on

I think it has something to do with the way the Internet is shared by the Mac Mini 2020 and their IP addresses having a different number in the 3rd category:

192.168.1.x and 192.168.2.x

Quoting from the article you linked: "You can share your media library with other computers on the same network. "

Remember that my AppleTV successfully streamed my Media Library when both the Mac Mini 2011 and AppleTV were connected to the same WiFi.

Both devices are on the same 5Ghz WiFi.

What do you mean by separate subnets; is that my problem? How can I fix it?

Thank you for that article: I now understand subnetting; but the article does not address my issue: how to get my two devices on the same subnet.

Remember, I am only using one hardware router.

...or to somehow link the two subnets together.

One hardware WiFi router and the Mac Mini 2020 with its Internet Sharing acting like another sub router.

Anyone???