I've long had a workflow in Alfred for adding things to my grocery list in Wunderlist. With Wunderlist being retired, I've switched a couple of shared-with-family lists to Todoist, and it's mostly okay; Todoist is much less of a good tool for just making lists, as it's oriented to projects  and lifestyle methodologies, but is good enough for what we need right now.

So I re-built my workflow in Alfred! All you need is a workflow that runs a bash script, and use the following for the code:

  curl https://api.todoist.com/sync/v8/sync \
  -d token=YOUR_TOKEN \
  -d commands="[{\"type\": \"item_add\", \"temp_id\": \"$(uuidgen)\", 
	    \"uuid\": \"$(uuidgen)\", \"args\": {\"content\": \"{query}\", \"project_id\": OPTIONAL}}]"

YOUR_TOKEN is found on the settings -> integrations page of your Todoist account. Specify a project ID if desired (I use the ID of my 'groceries' list as a default here). Otherwise omit the project argument. You can find the project ID by viewing the project in your browser; it will have a URL like https://todoist.com/app/#project%2F123456789%2Ffull, where the 123456789 is your project's ID.