It's normal for cats to have diarrhea after deworming. Diarrhea or soft stools are common symptoms after deworming. Usually, the deworming medication irritates the intestinal epithelial cells, leading to an imbalance in the gut microbiota and causing diarrhea. The diarrhea will gradually subside after deworming is completed. 
Things to note when deworming your cat:
1. Most deworming medications must be used on animals around 2 months old. Choose deworming medications specifically for cats. Do not feed human deworming medications, as it is difficult to control the dosage of human deworming medications for cats, and it is easy to give too little or too much.
2. Oral anthelmintic medication can be taken with food or after meals.
3. When using topical insect repellent, avoid bathing for 72 hours before and after application. Bathing reduces sebum secretion from the skin, thus decreasing the effectiveness of the medication's penetration and diffusion.
