Over 14,000 published articles suggest otherwise:
https://www.ncbi.nlm.nih.gov/research/coronavirus/docsum?fil...
https://www.ncbi.nlm.nih.gov/research/coronavirus/docsum?fil...
https://academic.oup.com/nar/article/51/D1/D1512/6814452
Yes there are general challenges in research, but not sure how that really changes the argument that there's significant amounts of research in this area and novel peer-reviewed findings.
These syndromes are best described by their respective pathogen: https://www.nature.com/articles/s41591-022-01810-6
EDIT: Sorry, you were talking to someone else. Disregard this comment.