.dotnetcore 3.1 vsdbg "Failed to launch debug adapter"/"Operation was canceled"

Question

I'm attempting to remote debug a console application(service) on a linux box using Visual Studio 2019(16.9.6). However, after VS attaches to the linux box(ssh), it will wait for a bit, then exit with "Failed to launch the debug adapter... The operation was canceled".

It suggests that there may be additional information in the Output window, but there's nothing there. I tried also creating a Visual Studio log with the log switch, but it contains nothing related to the remote dbg session.

Is there a way to log what is happening on the linux box when vsdbg is run? I don't even know if the "canceled operation" in a local operation or a remote operation.

* I've been debugging this software for months using all the same software, computers, VS, everything. I just came in one morning and this is what I found. *

I can connect using the gdb option, but not the managed option that I need.

I've also re-downloaded vsdbg and reinstalled it in case it was broken. Nothing changed, same problem.

Visual Studio 2019 (16.9.6) on Windows 10
Ubuntu 18.04 ARM64
C# 4.8

Any pointers?