iPhone
When changing iPhone to factory settings, will data be lost on other devices linked via the Cloud?
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No, the data on your other logged in devices will be safe on their hard storage.
See here for more information: https://support.apple.com/en-us/HT201274
Also, if you are planning to sell or give away a device, you should remove activation lock first.
See here for more information: https://support.apple.com/en-us/HT201351