WARNING: Do Open iCloud.com files using Microsoft Edge

Opened iCloud in MSFT Edge, opened Numbers file, worked on file and saved. Microsoft converted the file, when saving to an HTML file, which no longer allowed it to open in Numbers. All previous savings gone, spent 3 hours with Apple techs trying to recover using numerous approaches but unable to recover. Tech noted that others types of files, like .jpg, also have expereinced this same issue. MAJOR PROBLEM.