My take is slightly different. Do you see the list of clinical trials? They are throwing everything at this hoping something, anything will hit. They got nothing right now, not even a real idea.
Because Long-Covid probably isn't a syndrome or metabolic condition that can be regulated or adjusted. Long-Covid is probably going to be the result of actual damage.
There are all sorts of damages C-19 could cause that would be permanent but subtle. Brain damage being chief among them.
The bitter truth is that there are no treatments that "cure" permanent damage. In medicine, when you cannot cure the disease you treat the symptoms.
You look for palliative care treatments that will improve quality of life. That's why you are getting supplement makers like this doing clinical trial studies.
Long Covid is going to be a chronic condition in the population for the rest of the century. Shin did an earlier article estimating 5-10% of the population at any one time will carry damage from Covid infections.
This is in line with the damage loads earlier populations used to carry from things like tuberculous, syphilis, parasites (worms), and polio. It just seems jarring because we got used to public heath measures producing healthy populations.
Consider that list of clinical trials. That's a "throw everything at the wall and pray for a miracle" list.