Open HEIC without converting
If you only want to look at the files and not pass them on, you do not need to convert. You need a decoder.
The extension from the Microsoft Store
Search the Microsoft Store for HEIF Image Extensions. It installs in a minute, after which File Explorer shows thumbnails and the Photos app opens HEIC files. The catch: the image data also needs the HEVC Video Extension, and that one costs about a euro.
Where it still falls down
The decoder helps your computer, not the rest of the world. The moment you email a photo, upload it to a form, take it to a print shop or drag it into a document, the other side meets the same file it cannot open.
When converting is the better answer
If you only want to look through them yourself: install the extension. If you want to send, print, archive or still be able to open them in ten years: convert once to JPG and the question is closed for good.
Convert HEIC photos to JPG — right in your browser
Switch off the wifi before you start if you like. It keeps working — the conversion happens inside this window.
Select photos