an access_token which is a 32 char token and an id_token which seems to be a jwt token that contains my google information.
Which of these should I send to my backend. Should I send the access token and then use that to get the user id? Or the jwt token and decode it to get the userId
If you are looking to send your backend API an access token you should register it and add the identifier as the token audience. Here is an FAQ about it: