l-arginine has been used by people in this forum. Sometimes it makes things worse. Other times better. And right now I'm too fogged to do better explaining this But I thought it was interesting to see l-arginine plus vitamin C improve things for long covid patients
https://pubmed.ncbi.nlm.nih.gov/36501014/
https://pubmed.ncbi.nlm.nih.gov/36501014/