Noted for me adding tuneling at proxmox lxc.

Open proxmox host shell and open /etc/pve/lxcnumber/lxc.conf (/etc/pve/100/100.conf) and then add this

lxc.cgroup2.devices.allow: c 10:200 rwm
lxc.mount.entry: /dev/net dev/net none bind,create=dir

and then
chown 100000:100000 /dev/net/tun

after that reboot the container and voila success if problem still occure change dns setting add to the dns server

Thats it, its works for me

Happy coding and Salam ngoprek