Need more information since I don't know how to reproduce that locally.

For a start, can you provide the logs (stderr) that the server produces on start?

FWIW, other have reported similar behavior for other language servers.
See sublimelsp/LSP-volar#38 (comment)

Of note, during initialization, a blank cmd.exe window running node.exe pops up for a split second before it's gone. This doesn't happen with the other Node-based language servers I use.

You could try enabling disableAutomaticTypingAcquisition (see https://github.com/typescript-language-server/typescript-language-server#initializationoptions). If the problem goes away then we would know which process triggers the console exactly.

The only related thing that has changed (I believe) is that we never use the spawn method for creating the typescript process but always fork the parent process (see more info about differences in https://www.geeksforgeeks.org/difference-between-spawn-and-fork-methods-in-node-js/).

If that causes the console to pop up then I'm not sure if there is any way for me to control that.

Also you should provide the command line arguments that you use to start the server. That would make it clear whether your code was using fork method before.

Thanks, I can confirm that enabling disableAutomaticTypingAcquisition does solve this.

For reference this is the place where Typescript starts that process: https://github.com/microsoft/TypeScript/blob/e2c89af335e98003fa3a1cf8ec2acbd41add8a68/src/tsserver/nodeServer.ts#L510-L510

child_process.fork has a windowsHide option to prevent the console from popping up on Windows so TypesScript could use that. Though I don't really understand why forking a process there shows the console window while this doesn't happen when this server launched the tsserver process. It also doesn't use windowsHide:

@rchl from the docs it looks like fork doesn't have the windowsHide option, spawn does though.

Right, missed that.

BTW. What is the full command that you are running to that this server?

Initially:
node /node_modules/typescript-language-server/lib/cli.js --stdio

Then from the logs I see the command for tsserver is:
node /node_modules/typescript/lib/tsserver.js --logFile ts-logs.txt --logVerbosity verbose --cancellationPipeName /private/var/folders/_4/7kl16n5n3sxfwtjpyzsslsdr0000gn/T/a557efdc706754ca0d9ed63a01ed498c/tscancellation*

I don't really know why does this happen for you.

Even though I've provided a workaround, I think we could still try to figure out what and why exactly happens here but I'd need to defer that to you or someone else since I don't have a way to look into it.