>> A coagulant is typically added to turn the milk proteins into solid curds — in many cheeses, that coagulant is an enzyme called rennet, which is traditionally taken from an unweaned calf’s stomach lining, although vegetarian rennet, derived from molds or plants, is used in some cases.

"Traditionally" rennet was taken from an unweaned milk animal's stomach (not just a calf's stomach. Some people make most of their cheese from ewe's and goat's milk).

Fast-forward a couple thousand years and in modern times, most rennet in commercial cheeses is the product of fermentation by cute little bacteria cultured in cute little bacteria incubators:

... Because of the above imperfections of microbial and animal rennets, many producers sought other replacements of rennet. With genetic engineering it became possible to isolate rennet genes from animals and introduce them into certain bacteria, fungi, or yeasts to make them produce recombinant chymosin during fermentation. The genetically modified microorganism is killed after fermentation and chymosin isolated from the fermentation broth, so that the fermentation-produced chymosin (FPC) used by cheese producers does not contain a GMO or any GMO DNA. FPC is identical to chymosin made by an animal, but is produced in a more efficient way. FPC products have been on the market since 1990 and, because the quantity needed per unit of milk can be standardized, are commercially viable alternatives to crude animal or plant rennets, as well as generally preferred to them in industrial production.[12] ...

Source:

https://en.wikipedia.org/wiki/Rennet#Fermentation-produced_c...

But, somehow, everytime I read an article about vegan cheese it seems to lead with the outdated information that rennet is, like, normally, made with the stomach lininig of unweaned calves.