'delete some files to make more space'

Hi Tom Cray,

Thanks for posting in Apple Support Communities. To clarify, are you referring to iCloud Drive or only iCloud Photos? Some steps may vary a bit depending on which services you're using.

You should still be able to see content on your other devices if your iMac shuts down. Content would only be deleted from iCloud if deleted from your Mac manually. Which other devices are you using?

If you have another Mac and want to access iCloud Drive files from this Mac, take these steps from Upload and download files from iCloud Drive on iCloud.com.

"Download files

Changes you make to a downloaded file appear only on your computer unless you subsequently upload the file to iCloud Drive.

• In iCloud Drive on iCloud.com, select the files you want to download, then click  in the iCloud Drive toolbar.
• The files are downloaded to the location specified in your web browser’s settings."

You might also find Download iCloud photos and videos helpful since you mentioned videos. Guidance below is from that article.

"On your iPhone, iPad, or iPod touch

1. On iCloud.com, tap Photos. 
2. Tap Select, then tap a photo or video. To select multiple photos or videos, tap more than one. To select your entire library, tap Select All.
3. Tap the more button  .
4. Choose Download, then tap Download to confirm. 

If your photos download as a ZIP archive, learn how to uncompress the folder on your iPhone, iPad, or iPod touch. 

On your Mac or PC

1. On iCloud.com, click Photos and select a photo or video. Hold the command key on your Mac or control key on your PC to select multiple photos or videos. 
2. Click and hold the download button  in the upper corner of the window. If you want to download your photo or video as it was originally captured or imported, choose Unmodified Original. For JPEG or H.264 format — including edits, and even if it was originally in HEIF or HEVC format — choose Most Compatible.*
3. Click Download."

You may also be able to create a Time Machine backup while your Mac is working properly so that you have your data on an external device. Check out Back up your Mac with Time Machine.

All the best.

Tom Cray,

If you're referring specifically to iCloud Drive and other iCloud services, that content should be available on any device that supports iCloud and that you're using with the same Apple ID. You could try signing into the iCloud website using a computer to verify that your content is all available there: iCloud

We hope that answers your question. Let us know!

Cheers.