Can I use my mac mini as an apple tv

You can "Airplay" from a Mac to an AppleTV or any "smart TV",

but the reverse is not true. An even at that, the Mac must

first have the proper hardware to support it and must have a

macOS version that supports it, i.e. you cannot just install "Airplay 2".

There may be a third party app to do it. Check the App Store.

As you already know, your computer can play Apple TV . I am assuming that you have an account set up. That said, if you can connect your computer to a smart TV as has been noted, you can also set us that smart TV to directly access Apple TV via the internet. Smart TVs have Wi Fi access to the internet, or you can run an ethernet cable. I recommend that you check the TV manual to see how to do this. Sometimes initially setting up the TV's interface can be annoying, but just be patient and follow instructions. Good luck.

Why not try it out?