Depois de pesquisar e testar as coisas por algumas horas, essas etapas funcionaram para mim. Eu tive que ligar para o meu telefone como um hotspot para provar isso porque ele não funciona quando conectado ao mesmo hotspot wifi como o roteador que está executando o servidor vpn. Espero que isso ajude alguém.
# install these packages in ubuntu terminal
sudo apt-get install openvpn
sudo apt-get install network-manager-openvpn
sudo apt-get install network-manager-openvpn-gnome
# download the client files from the router as
# a zip file and extract them to my Downloads directory
# open network > edit connections > add >
# import a saved vpn configuration > select the client.conf file
# that was extracted in the Downloads directory
# edit the vpn connection and set the gateway port to :12973
# (same as is configured in the router's vpn settings)
# change type to TLS
# select client.crt that was extracted in the Downloads dir
for user certificate
# select ca.crt that was extracted in the Downloads dir for ca certificate
# select client.key that was extracted in the Downloads dir for private key
# click Advanced
# change custom gateway port to 12973
# change virtual device type to TUN
# check the checkbox to accept authenticated packets from any address