How can I upload files to iCloud from an external drive?

Hello,

I don't have enough disk space on the primary disk to transfer from one cloud to another, so I need to use an USB drive to upload files to iCloud.

What options do I have?

1 - I don't see any possibility to upload files from an external location...

For example, even with the Desktop folder, which is not in sync by default, I don't see any option in the menu to share that file to iCloud...

2 - Would it work with a symbolic?

3 - It's obvious that once uploaded, these files won't be synced on this disk.

So, I'm searching also for a solution to download these files on an USB drive later.