Your device is running slow, but your antivirus software is not detecting anything. You are unable to copy or find files you know exist on your machine (this is commonly used as DRM to prevent the copying or redistribution of music, movies, or video games). Your device obviously has malware on it, but your antivirus software does not detect anything. Your device takes a long time to start up. Your hardware has stopped working correctly. Other devices (like your router) are reporting that your device is using it even if you are not actively using them.
Microsoft Defender will inform you if you need to run Microsoft Defender Offline.
On iPhone 7, you do not have to press the volume up and volume down keys at the beginning. On iPhone 6s and earlier, use the home button instead.
