As stated eariler, I would like the AC1200 box to act as an L2TP client, analogous to WireGuard client or OpenVPN client, which I already have configured.
The GL-inet webUI does not currently support configuring an L2TP client, but I’m certain it can be done in openWRT in the UI or via SSH at the command shell.
As an example, here is the Windows implementation of a GUI configuration for LT2P client: