As early as 2020, doctors who were treating Covid patients who required hospital care had observed that many of these patients were suffering from excessive blood clotting, which could result in large clots (which could result in a stroke or heart attack) or microclots in small blood vessels (which, if sufficiently numerous, could starve the tissues in the vicinity of oxygen and lead to organ failure).
The initial cause for the excessive clotting was found to be inflammation of the inner linings of blood vessels due to the interaction of the spike protein* from the virus SARS-CoV-2 with the ACE-2 receptors of the cells lining the blood vessels. This damages the inner lining of the blood vessels and releases clotting factors that trigger a clotting cascade.   
By July 2020, it had been hypothesised that the clotting problems of seriously ill Covid patients was due to “an amyloid form of fibrin that is highly resistant to degradation”. 
More recent research suggest that for people who have “Long Covid”, that is, symptoms such as “fatigue or muscle weakness, being out of breath, sleep difficulties, and anxiety or depression” that persist in people who have recovered from the acute phase of a Covid infection may be due to “blood clots can block microcapillaries and thereby inhibit oxygen exchange”. 
Tests comparing blood samples from people with Long Covid as well as healthy people and people with other conditions showed that “plasma samples from Long COVID/PASC still contain large anomalous (amyloid) deposits (microclots).” 
This being said, some people with have Long Covid are extremely ill with many more symptoms, including cognitive problems (that may be described as “brain fog”) and POTS – a distressing condition in which people can experience a racing heartbeat when they stand up that may be accompanied by a feeling of faintness and/or palpitations, among other symptoms, severely limiting the time that they are able to stand up.  POTS has many possible causes , one of which is Mast Cell Activation Syndrome (MCAS), which has also been theorised to be play a role in severe Covid and Long Covid as early as 2020.  (Some Covid shot injured people have also been diagnosed with POTS.) It is interesting to note that low oxygen levels can be a trigger for mast cells (a type of white blood cell) to “degranulate” and release a variety of chemicals that can increase inflammation. Mast cell degranulation may result in the release of platelet activating factor which makes platelets “stickier”, thus potentially worsening any existing problem with blood clotting.
There are various ways of approaching the treatment of persistent microclots.
A clinic in Germany offers HELP Apheresis which is a technique of removing blood from the body, separating it into red blood cells and plasma and then filtering the plasma to remove fibrin and finally returning the red blood cells and cleaned plasma to the body. A British respiratory medicine specialist who had caught while treating Covid patients in 2020 and became very ill with Long Covid attributes a significant improvement in his health to this treatment.  (He had so much fibrin in his plasma that it clogged the filter.)  Interestingly, this doctor had had a normal d-dimer blood test prior to this treatment presumably because his body had been unable to break down the amyloid form of fibrin in his body.
One treatment option for microclots and excessive fibrin in the blood is to use proteolytic (protein-digesting) enzymes. Taking enzymes of this type between meals allow them to absorbed into the bloodstream (rather than used to assist in the digestion of food).  There are a number of different enzymes available that could be used for this purpose, including serrapeptase, nattokinase and bromelain (derived from the stem and core of pineapples). Of these enzymes, bromelain degrades fibrin and may also have anti-amyloid properties.  
Serrapeptase and nattokinase also have fibrin busting and anti-amyloid activities. 
IMPORTANT NOTE: This article is intended to provide information; it is not medical advice. If you are interested in taking enzymes, please consult a health professional about their suitability for your situation.
* Unfortunately, the choice to develop vaccines that either contained a version of the spike protein from SARS-CoV-2 (or were designed to trick the body into synthesising the spike protein from SARS-CoV-2) means that these shots have the potential to cause excessive blood clotting and illness as a result. Live blood analysis (in which a small sample of blood is put on a glass slide and a coverslip placed on top and then the sample is observed using a darkfield microscope) has shown what looks like fibrin in the blood of some patients who have received Covid shots.
 A more general reader friendly article is this one: https://oatext.com/probable-causes-of-blood-clotting-driven-by-sars-cov-2.php
 Amyloid form of fibrin https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7403995/
 https://nexusnewsfeed.com/article/health-healing/are-fibrinolytics-key-to-preventing-clogged-arteries/ (Note regarding timing of taking enzymes: “Also, remember that they need to be taken on an empty stomach, at least one hour before or two hours after meals containing protein.” Also this suggestion: “Fibrinolytic enzymes are ideal for targeted usage; as mentioned, if you intend to use them daily, be sure to alternate through the following types so you don’t develop a sensitivity or allergy to them.”) This more recent article by Peter McCullough is worth reading: https://petermcculloughmd.substack.com/p/dissolution-of-spike-protein-by-nattokinase
Note: This is a slightly revised version of an article that was first published in issue 45 of The NZ Journal of Natural Medicine.
NZ specific information on Long Covid from an organisation supported by the University of Auckland may be found at this link: https://www.nihi.auckland.ac.nz/node/1221
About The NZ Journal of Natural Medicine:
The NZ Journal of Natural Medicine is a quarterly print magazine that covers a range of natural health related topics, including articles about a variety of therapies that can help maintain or regain good health. The Journal also includes articles about treatments and/or environmental toxins that may be hazardous to your health. Our online shop where you may subscribe (If you are in NZ or Australia), or by PDFs is: https://naturalmedicine.net.nz/shop/
IMAGE CREDIT: Thank you to sh0dan from https://www.freeimages.com/ for the use of the image of the pineapple, the source of the enzyme bromelan.