Dedicated Ubuntu bedrock server with "Multiplayer Game" off?

I'm attempting to set up a Bedrock LAN-only server for crossplay on PC + Nintendo Switch.
I have the server up and running in an Ubuntu VM.
I changed the DNS server on my Switch to that 104.x address that allows you to connect to private LAN servers on Switch.
I can connect on both PC and on Switch successfully.

However, on Switch I can only seem to use my account that's tied to my Nintendo Switch Online Individual membership. When I grab a second Switch controller, press + and attempt to join in split-screen, I get a message saying that "Multiplayer Game" needs to be disabled (which is greyed out, of course as it is even for Switch-hosted servers and needs to be edited from the worlds menu instead of in-game). I assumed this setting would be tied to the server.properties "online-mode" setting, but setting that to "false" didn't change anything.

Does anyone know how to disable "Multiplayer Game" for a Bedrock dedicated server? Is it somehow set in the world .dat file itself, or is it a different option in the server.properties that I'm not seeing?

TIA