system installation – Proper way to install Ubuntu (Server 21.04) with PPPoE?

Recently I downloaded and burned ‘ubuntu-21.04-live-server-amd64.iso‘ to an USB-stick.
I need PPPoE connection while installing (as my router is in bridge mode). says to add (grub) boot-command-line-option ‘modules=ppp-udeb‘.
So I interrupted the boot-process pressing ‘e’ and made up this:

setparams 'Ubuntu Server'

  set gfxpayload=keep
  linux /casper/vmlinuz --- modules=ppp-udeb
  initrd /casper/initrd

At installation after keyboard-selection comes ‘detection of network hardware‘, where the interface is found and is selected to (IPv4) DHCP.
PPPoE configuration does not appear (and DHCP obviously fruitless).

So, what is the proper way to install Ubuntu (Server 21.04) with PPPoE ?