Trust me, they can't do sh*t about your experience letter, letters these days are anyways factual with just the joining and relieving date, designation etc and in some cases UAN no, last drawn salary etc.
They threaten employees that if they don't accept the lay off, they will be given a termination letter instead of an experience / relieving letter.
You have already accepted that you are being laid off. They can't dare to fall further and eff your BGV because if you are wronged beyond this, they run the risk of you going on social media and exposing their mistreatment of employees. Don't fear them beyond a point, they also have things to be scared about.
My friend was let go from a 'prestige' firm within 6 months of her joining, a lot of new joiners were let go because of the economic downturn. Her manager asked her to complete a deck, which she did and he then asked her to work beyond 5 PM on a Friday and do some client calls since she knew the client best. She flatly refused and said that if her work mattered that much, she shouldn't have been laid off and that she had been working round the clock earlier while only billing 8 hours but during the forced notice period, she wouldn't work a minute beyond the official hours. She sent me a screenshot of the guy's horrified expression. Totally worth it. Bridge burnt, yes, but the question to ponder over is, if there even was a bridge in the first place?
Focus on your job search and relax a bit, you deserve it.