iPhones save photos in a format called HEIC (HEIF) by default, and Windows doesn't support it out of the box. So when you move an iPhone photo over to a Windows PC, you often get no preview and just a "this file can't be opened" message.
According to Microsoft's own support documentation, neither Windows 10 nor 11 can open HEIC by default, and the Photos app will prompt you that "an extension is required." If that happens, try installing both the "HEIF Image Extensions" (free) and "HEVC Video Extensions" (paid, about $0.99 in the US) from the Microsoft Store. The reason a photo format needs a video extension is that HEIC photos are internally compressed using HEVC. (Some recent Windows 11 builds ship with the HEIF Image Extensions included by default.)
If paying for an extension feels like overkill, there's a simpler route. In your iPhone, go to Settings → Camera → Formats and switch to "Most Compatible" so future photos save directly as JPG. For photos you've already taken, CornButter converts them right in your browser — no install, no payment, just upload the file and it becomes a JPG in seconds, ready to open anywhere on Windows.
Convert HEIC to JPG — you can upload several at once.