Jazzylis Said:
"I Just purchased a Mac mini, will I be able to transfer the data from my iMac to the Mac mini even though it has that old high sierra operating system?"
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What to Do:
1. Back up your Mac: Start by creating a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the upgrade.
2. Perform an Upgrade:
Go Here, and see if you can upgrade: How to get old versions of macOS - Apple Support
3. Migrate and Reinstall Data and Apps:
Once all is complete, migrate it over from the Time Machine Backup you created in step one. If required, request from the developers new keys for their software, informing them that your computer crashed. Ask for 64-bit installers, if looking to install