how do I stop using iCloud and keep the files on my MAC

All of your files are on your Mac, unless you elected to optimize storage, in which case your oldest files may have been offloaded if space was needed on device. Go to system settings - Apple ID - iCloud to review iCloud Drive and settings (and to turn off iCloud Drive sync)

leonardml Said:

"how do I stop using iCloud and keep the files on my MAC"

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Disable [an item] in iCloud Settings:

1. Go to: System Settings
2. Tap: Your Name (top Item)
3. Tap: iCloud
4. Tap: an item (so that it is greyed-out)

You are welcome.