Migrate from TeamDrive to Another TeamDrive

should work, but just to make sure that this is actually enabled - try setting it in your config instead. Use:

server_side_across_configs = true (note the different formating - copypaste it)
Put this in the bottom of each of your 2 remotes
save the config
remove " --drive-server-side-across-configs=true" from your command
then retry and see if the result is the same.

Are both of these drives accessibe under "shared drives" (previously called teamdrives) in the Google Drive website. In other words - is the user a member of both teamdrives?

I ask because it can be a bit confusing now to talk about shared files and shared drives which are fundamentally different things. Feel free to crop a small image from your Google Drive website that lists them just we can see this looks as expected.