plex-media-player has been deprecated in favor of Plex for Desktop and Plex HTPC.
brew install --cask plex
OR
brew install --cask plex-htpc
plex-media-player is built for Intel macOS and so requires Rosetta 2 to be installed.
You can install Rosetta 2 with:
softwareupdate --install-rosetta --agree-to-license
Note that it is very difficult to remove Rosetta 2 once it is installed.
