I have already resigned and through HR my manager is forcing me to work unless disciplinary action will be taken.

Don't take it as negative. Take it and do whatever you can do. Every single aspect counts in your career. May be that person or that team help necessary in future. Not only for you it's for for every one.

Don’t work they can’t do anything

Take the work and whenever they say what the update tell them it's in progress and it's a new domain, so will take some time. Also if you have a dependency try to offload it to you replacement

Are you not getting paid during notice period? Grow up, be professional man… work till last working day.

Stay calm and do work whatever possible don't get into argument this is common scenario in all places

Nothing will happen enjoy your life

Bro notice period does not mean you can chill and not do any work. It means that you are giving support to company when they look for your substitute or replacement. This is a required thing and is your responsibility. As for them giving tasks out of your domain, take them, try to do them, but you don't need to go out of your way to complete them. If you can, do it, if you can't, no one can blame you. But downright rejecting is not a behaviour people will appreciate.

How long it's been since you resigned?

Just have a talk with hr and tell them you are giving me mental harassment, i won't be able to tolerate this

I will say you can work at least for first 30 to 50 days then you can reduce your work hours