From 2011:
Fibrin is the main structural component of the thrombus. The conversion of fibrinogen to fibrin by thrombin leads to one of the most remarkable processes in biology in which fibrin spontaneously forms a gel by producing fibers that grow longitudinally as well as laterally, with branch points forming and interconnecting the fibers leading to the formation of a 3-dimensional network that binds platelets and traps other blood cells. Even after the gel point, the architecture of the fibrin network can change quite dramatically.
Something to keep in mind as some papers have discussed how spike protein may dis-regulate fibrin behaviour as well as causing damage to the endothelium.