Run the following commands in terminal
# update software repositories
sudo apt update
# install software updates
sudo apt upgrade -y
# install some prerequisites
sudo apt install apt-transport-https ca-certificates
# get the latest .deb download URL
regex='"build":"linux-aarch64","distro":"debian","url":"(https:\/\/downloads\.plex\.tv\/plex-media-server-new\/[^/]*\/debian\/[^/]*_arm64\.deb)",' && response=$(curl -s https://plex.tv/api/downloads/5.json) && [[ $response =~ $regex ]] && downloadURL="${BASH_REMATCH[1]}"
# download latest plex version
wget -O ./plexmediaserver.deb $downloadURL
# install plex media server
sudo dpkg -i ./plexmediaserver.deb
# run plexmediaserver service on system boot
sudo systemctl enable plexmediaserver.service