The answer to your question depends greatly on the context surrounding the civilization therein.
On the one hand, it would be really easy for there to be detailed cultural mythos and superstitions surrounding said creatures. Just look at how people treat bears today: we make them the subject of our folktales (Goldilocks and the Three Bears), tell stories with them, yet in most cases also have a pretty healthy fear/respect for them and will do just about anything to avoid having them cross our path (bells, bear spray, etc.). Or look at how people in the Kamchatka Peninsula treat Siberian Tigers. The people there have all sorts of superstitions about tigers, such as if someone tries to poach a tiger's kill it will remember you, track you home, and make your life miserable, but how true these are is sometimes unclear. On the one hand, it would be very likely for the locals to have all sorts of superstitions about the local wildlife, especially if they rarely see them and don't know much about them.
However, at the same time it is super unlikely that no one would be studying these creatures in a scientifically rigorous manner, assuming your society is similar to present-day society in technology. To get to a modern or "100 years beyond ours" level of technology, a society needs to have an outlook that favors investigation and the scientific method, because otherwise...well they wouldn't be able to maintain their technology or at best descend into cargo cultism. But what this means is there is no way they would leave the creatures alone.
Let me put it this way, as someone who has firsthand experience with biology, biologists, and a general interest in masquerade tropes. The reason scientists generally don't believe in Bigfoot and other cryptids isn't because of any agenda or desire to believe something doesn't exist, it's because there isn't any reliable evidence. The minute anyone found a reasonably decent specimen suggesting that there was some undescribed hominid present in the woods of North America, scientists would descend on the Pacific Northwest en masse, smelling glory and easy grant money. And virtually any fictional monster would leave traces that most scientists would instantly recognize as something unusual, and therefore worth studying. Even if some pooh-poohed the idea, others would pursue it, and it only takes a few to make a breakthrough that forces the floodgates open.
What this means is, presuming your creature existed, is it would be near impossible to get scientists to not study them given the general publish-or-perish atmosphere. Which means scientists would most likely not exist in your setting.
Even if, say, your creatures were super hard to find, or could not be kept in captivity, or spontaneously decomposed upon death, there would still be people who study them. There are animals today that people have seen less than a few dozen times that people study (e.g., megamouth sharks, certain species of squirrels and opossums). Other species do not do well in captivity (e.g., great white sharks, most whales), so people stick cameras on their back. Even if they spontaneously decompose, well, sharks and soft-bodied cephalopods do that in the fossil record, and there are people who make their entire career studying fossil shark teeth.
Also note that even IRL wildlife has some mysticism and superstition about it, even in the last 100-200 years when people were studying it via the scientific method. At the turn of the 20th century amateur naturalists still spoke of "elephant graveyards" in Africa and India as if they were a real thing, though they sort of talked about it like it was more legend than truth (check out old articles from Journal of the Bombay Natural History Society for a few examples). Until 1975 almost no one knew where monarchs went during the winter, despite seeing huge swarms of them depart to the south every year.* We still don't know how great white sharks or whale sharks mate or give birth (other than they give live birth), despite these being some of the largest creatures in the ocean.
TL;DR: You're probably going to have to get rid of all scientists, as well as remove any sort of attitude favoring the scientific method among your populace. Curiosity about the natural world does not mesh with the idea of a species that is well-known in folklore but no one is interested in studying. I have no idea how you would maintain a society with a tech base 100 years beyond ours with that, though.
* - local inhabitants of the mountains of Mexico knew about them, but most Mexican biologists seemingly didn't, because it wasn't well known at the time.