celia16, There's plenty of cystiene-rich food out there but it comes with two problems: I don't know how much you'd have to eat in order to benefit. Maybe foiurteen scrambled eggs and a full brisket of beef for breakfast... (joking, of course, but you get the idea.)

Second, the cystiene in food form passes right through the digestive system. Your body has to make its own, or make up the shortfall (common with long COVID) with supplements.

NAC has benefits for brain health (alertness, memory, cognitive function - in my experience a boost but not a return to pre-COVID, kidney and liver health, in flushing out stuff that shouldn't be there.

If you try it, please let us know how you do. The supplement is cheap so it isn't as bad as other therapies in that regard.