Uploading Photos to iCloud Photos

I have a bunch of photos on my external hard drive. I want to upload them to iCloud photos to back them up, and make them available in all of my Apple devices. Is this possible?

This is NOT backing up the photos on my iPhone. I already do that.

I don't need a copy of my photos on my devices.

I read Apple help pages but I couldn't find the answer to my question.

Thank you in advance.

Best,

Elif