Microsoft hides file extensions in Windows by default even though it's a security risk that is commonly abused by phishing emails and malware distributors to trick people into opening malicious files.

View file extensions in File Explorer Never be confused about file types I deal with many different file types on a daily basis, whether they are JPEGs, PNGs, PDFs, or Photoshop files.

Show or Hide Extensions for All Files in iOS Since iOS 11, Apple's Files app has made file management a more realistic proposition on ‌iPhone‌ and ‌iPad‌.