Really hard to get proper funding for LDN. It is an already incredibly cheap drug in a minute dose... this treatment is not exciting to anyone except patients and a few passionate researchers.
Lots of studies showing "interesting results, needs more investigation" but high quality studies are very slow to come...
https://reddit.com/r/covidlonghaulers/s/2SzkM5ca5K
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9250701/