Going forward, the following thread post describes @yonah_ag's folder structure (and now, mine, too) for file versioning. This might help if the problem arises in the future. (Sadly, if you're not already doing it, it cannot help NOW.) https://musescore.org/en/node/371355#comment-1266913
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It may be in a hidden back-up folder. Look up how to view hidden folders for your OS.
Finding backup files:
How to recover a backup copy of a score
How to recover a backup copy of a score (1.x)
Going forward, the following thread post describes @yonah_ag's folder structure (and now, mine, too) for file versioning. This might help if the problem arises in the future. (Sadly, if you're not already doing it, it cannot help NOW.)
https://musescore.org/en/node/371355#comment-1266913