How to delete photos and documents on one MacBook

Ramimur wrote:

I've run out of storage space on my MacBook Pro 15" Intel 2018 14.5. I want to delete documents and photos from this Mac to gain storage and leave them in iCloud.

iCloud is a sync service...

You can "optimize" your storage on iCloud

Optimize storage space on your Mac - Apple Support

Or use some external storage device to remove them from your Mac— thus freeing up storage space

If you delete photos from any Photos library connected to iCloud Photos – whether that library is on a Mac, iPhone, or iPad – that is taken as a request to delete them everywhere, including in iCloud.

Going into your Mac's Photos Library and blindly deleting things while it is connected to iCloud will make you lose your photos.

There are a few courses of action you can take, but you must proceed carefully.

• One would be to copy photos somewhere outside of iCloud Photos, then delete the iCloud Photos copies. The photos would disappear from the Photos libraries on all of your devices, but would be available from the places where you had copied them. (Related to this: It is possible to have multiple Photos Libraries on your Mac, only one of which syncs with iCloud. Apple doesn't make it convenient to move photos from the main library to, say, your secondary library on an external drive. But it is possible.)
• Another would be to disconnect this Mac from iCloud Photos. It would no longer get syncronization updates from your other devices, but once the photos on the Mac were strictly local, you could delete them without affecting the copies in iCloud or on other devices.
• Another would be to move the main Photos Library on your Mac to an external drive. This probably would not be a great idea for a MacBook, since it is likely that you would have the external drive disconnected a lot. If you did this on a desktop where the external drive was mounted all of the time, then you wouldn't be depriving Photos of the chance to synchronize with iCloud in the background.

There's also the "Optimize Mac Storage" feature of Photos that leroydouglas mentioned.

That one shouldn't cause you to lose your photos. It will just substitute lower-quality local versions of your photos for full-quality local versions of your photos, on the assumption that it can re-download the full-quality ones later.

The key is that you have to let that feature work automatically. You can't go in and start manually managing photos by deleting them, or the deletions will be synchronized, and you will lose your photos.