Seems the instructions are incomplete, at least they did not work for me using vscode 1.92.2 on macOS as the client.
I have applied the following command in my ~/.vscode-server directory:
cd ~/.vscode-server
find . -type f | xargs file | grep -w SYSV | cut -d: -f1 | xargs brandelf -t Linux
In addition to installing the devel/linux-rl9-libsigsegv port, I have created the following symbolic link:
mkdir -p /compat/linux/usr/local/bin
cd /compat/linux/usr/local/bin
ln -s ../../../bin/bash .
Without that link, the RemoteShell option made SSH start the Linux bash, but then the FreeBSD bash was started from /usr/local/bin/bash and the installation of the vscode server failed since uname reported FreeBSD when invoked by the FreeBSD bash.
In settings.jsonI have added the following parameters:
"remote.SSH.enableRemoteCommand": true,
"remote.SSH.useExecServer": false,
"remote.SSH.useFlock": false,
I'm not sure that all of those are required, but at least enableRemoteCommand is needed (else the RemoteShell option in ~/.ssh/config is ignored).
After these additional steps I got the vscode server working on FreeBSD-CURRENT - thanks a lot!