I'm going to leave my current company in a month as I have accepted an offer from another company and I'm currently working on the H1B transfer step. H1B transfer should take three weeks at the most. Recently my org had a restructuring and my manager has been changed leading to newer project and new team member and nowadays I spend most of my time onboarding myself onto the new project. I have couple of questions here:
What's the right time to inform the manager about my next move?
In the US, it's employment at will so you have 0 obligations:
Should I give my 100% into the onboarding? I feel low-key guilty on adding more burden to the team by doing work which will add no value at the end.
Nope, just do the bare minimum. It is indeed a waste of everyone's time to pretend like you're not leaving and are still grinding for a stellar performance review.
I recommend this discussion too: "How can I gracefully leave my job?"
I've given 1 month notice in the previous two jobs that I've left. I found that this gives enough time for your manager to go through all of the paperwork and meetings when someone leaves a company without feeling rushed. it also gives you enough time to wrap up any loose ends on projects and let your co-workers know that you are leaving.
Should I give my 100% into the onboarding?
It's not a good use of your time to continue the onboarding process. I would finish out your time by setting up meetings with your co-workers and letting them know that you're leaving so they know that everything's okay, and you are leaving on good terms. They might want to join you later on :)