The short answer: No.
The long answer: Mushrooms are spore-bearing fruiting bodies of fungi. They can grow underground, within trees, or even in decaying logs. Technically speaking, store-bought mushrooms safe for human consumption are also safe for cats to eat. Just make sure they are not cooked with salt, onion, garlic, or other harmful ingredients.
However, it is best not to serve mushrooms to your cat so that she does not get used to its umami taste and texture. This is because she may nibble on potentially dangerous wild mushrooms that she finds outdoors. These wild mushrooms may contain dangerous toxins such as amanitin, muscarine, psilocybin, and isoxazole.
Toxicity will depend on the wild mushroom your cat eats. Common symptoms of mushroom poisoning include vomiting, diarrhea, dehydration, electrolyte imbalances, decrease in heart rate, and severe drooling. Other types of wild mushrooms may cause unsteadiness, agitation, depression, and sensitivity to sound/touch/tremors. Additionally, some may result in appetite and energy decrease, yellowing of the eyes and skin, liver failure, and even death.
What to do if your cat accidentally eats mushrooms: If she ate a small piece of cooked mushroom, she should be okay. If you suspect that your cat ate wild mushrooms, observe her for the next 24 hours. More importantly, get her examined by the veterinarian immediately. If possible, bring a sample wrapped in a moist paper towel, so your vet can determine what kind of wild mushroom your cat ate.
In summary: Mushrooms do not contain any nutritional value for your cat, so it is best not to include it in her diet. To be on the safe side, remove the mushrooms you find in your backyard or around your neighbourhood. For paw parents who like taking their cats on outdoor walks and hikes, it’s best to use a harness so you can stop her from approaching and accidentally eating wild mushrooms.