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Welcome to the Apple Support Communities!
It sounds like you need to free up some space on your new iMac Pro. Did you set this Mac up by restoring from a Time Machine backup or transferring a user account with Migration Assistant? Have you updated your computer to macOS 10.15.6? Restart the computer to refresh it and reestablish a connection to the internet.
The "Other" category includes things like emails and text messages and their attachments, system files, application data, etc. The Review Files button in the Storage Management window will help you find the large files on your computer, and which apps were used to create them. It is usually best to go to the specific app, like your email application, and delete the attachments or files you no longer need from within the app.
Find out how much storage is available on your Mac

"Reduce Clutter
Reduce Clutter helps you to identify large files and files you might no longer need. Click the Review Files button, then choose any of the file categories in the sidebar, such as Applications, Documents, Music Creation, or Trash.
You can delete the files in some categories directly from this window. Other categories show the total storage space used by the files in each app. You can then open the app and decide whether to delete files from within it.
Learn how to redownload apps, music, movies, TV shows, and books."

If you want to keep the files, you can move them to an external drive. Confirm the files can be opened on the external drive before deleting them from your internal hard drive.
Use external storage devices with Mac - macOS User Guide
Move your Photos library to save space on your Mac
Take care.