What is the ruling on doubt and intrusive thoughts concerning the permissibility of imported foods, meats served in restaurants, gelatin in sweets, and products containing animal derivatives, especially given that the questioner lives in a Muslim country?

What you are suffering from is blameworthy waswasa (whispering from Satan), not praiseworthy piety. Abandoning what is known with certainty to be permissible due to delusions is a deception from Satan. Therefore, do not avoid any foods or anything else unless it becomes clear to you with certainty that they contain what Allah has forbidden. It is advisable to consult the counseling section on the website and a psychiatrist.