I am currently solving it by adding cd ../project before the real commands.

I'm not sure i fully understand the question, could you explain it in more detail pls?

I think this is similar to what I am looking for...where I have a workspace that has multiple folders. I need a terminal in each of those folders as they all have something that I need to start. So it would be awesome if there was a WORKDIR argument for convenience.

Structure

Workspace
  folder1
  folder2
  folder3

So could have something along the lines of

"restoreTerminals.terminals": [
{
   "splitTerminals": [{
     "name": "api",
     "workdir": "./folder1"
   },{
     "name": "ui",
     "workdir": "./folder2"
   }
   ]
 }
]

I've tried running something along the lines of

"restoreTerminals.terminals": [
			{
				"splitTerminals": [
					{
						"name": "ui",
						"commands": ["cd ../ui"]
					},
					{
						"name": "api",
						"commands": ["cd ../api"]
					}
				]
			},
			{
				"splitTerminals": [
					{
						"name": "shared",
						"commands": ["cd ../shared"]
					},
					{
						"name": "backend",
						"commands": ["cd ../backed"]
					}
				]
			}
		]

When this runs in actually gives some very strange results, even with the artificial delay set to 1000.
I end up seeing the following terminals where there are two high level terminals without any splits...and then some that are split but not named properly and an extra terminal thrown in o.O

api
api

-ui
-zsh
-zsh

-ui
-zsh

I'm struggling to think of a fix. This is a known new problem microsoft/vscode#45407

If anyone knows how to get around it, please help!

I like the @afreeland proposal.
My 5 cents:

Keep in alignment with the VS Code nomenclature

"restoreTerminals.terminals": [
{
   "splitTerminals": [{
     "name": "api",
     "workspaceFolderBasename": "folder1"
   },{
     "name": "ui",
     "workspaceFolderBasename": "folder2"
   }
   ]
 }
]

The commands accept array of commands you can have cd command to the work folder before main command.

"restoreTerminals.terminals": [ { "splitTerminals": [ { "name": "project-name", "commands": ["cd workdir","npm start"] } ] } ]