HEIC files - how to open or convert?

We took several hundred iPhone 8+ photos on a European vacation. Some are listed as HEIC format. If we edited then on the phone - they will open. If not edited - they will NOT open on the computer. Attempts to get apps form Microsoft, etc. Are not helping. Other than seeing what is missing, and then needlessly editing them on the PHONE, and then downloading again - any suggestions? Even the Users at MS are ranting about the uselessness of their add-on or apps to fix there!

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