I noticed that Chrome Version 86.0.4240.111 (Official Build) (x86_64) and Safari Version 14.0 (15610.1.28.1.9, 15610) on Mac OS 10.15.7 (19H2) does not play any item.
The App on Tivo and Android plays. When I download the Plex Player for Mac OS it also plays.
What is the issue with web browsers? Is there security software preventing to stream or a new features that Plex Media Server only talks to “signed” apps?