A VSCode/VSCodium extension to that adds a command to toggle Mocha it.only to the test the cursor is in.
cd ~/.vscode/extensions
git clone https://github.com/maxlath/vscode-only-test
This command can then be bound to a shortkey, by adding the shortkey to keybindings.json (in my set up, can be found at in ~/.config/VSCodium/User):
{
"key": "ctrl+shift+alt+o",
"command": "only-test.toggle"
}