I’m using an MacBook Air 2018, 13" Retina display running Mojave 10.14.6 (see earlier postings, Catalina trashed my system).
I’ve got an Apple external DVD drive (left over from a Mac Mini from a few years ago). The DVD player plays DVDs beautifully on the Air. The Air can send the output of the computer to my Apple TV (and its associated 55" LG TV set).
When I attempt to send the DVD output to the TV, the window on both the Air and the TV turn a solid Grey color. I can hear audio, but I get no video. I’ve tried various settings (mirroring the Retina Display, or the TV or…) Nope. Sending anything else - Safari windows, MacMail, Photos, iTunes - they all work. DVD - not at all.
I realize that DVDs are old technology and many movies are available for streaming. Many - but not all.
If I can’t get this working, it won’t be a tragedy. I’m trying this because my old DVD player died. If there’s an easy fix then I’d love to hear it! If not, I’ll survive.