How to stop a 6TB iCloud from downloading to internal 256GB hard drive?

According to Apple, iCloud is a syncronisation service AND a storage. See this page

What is iCloud? – Apple Support (UK)

You can buy for example 6TB costing you in Europe € 30. But if you want to store many TB's iCloud tries to download to my Mac mini M1 that has only 256GB.

I have my files (about 4TB) on an external hard drive and I want the same files as an exact copy on iCloud Drive. That is why I opted for 6TB iCloud. When at work I want to have acces to all my files via iCloud.com. "Access iCloud Data on the Web" is enabled.

When I try to use a file sync program, trying to sync between an external hard drive and iCloud, there is a problem as I get a message that there is not enough space. Of course there is enough space on the 6TB iCloud that I am renting from Apple, but not on the internal hard drive.

That is my experience.

I probably do not quite or correct understand: System Setting > "Account Storage" and "Optimise Mac Storage" The last one I have enabled and I know that I can, in my iCloud Drive click "remove download" so there only stays a link on iCloud Drive and not the file itself. But that does not solve the sync problem.

• Probably I do not understand correct the use of iCloud and/or iCloud Drive. Would very much appreciate a thorough explanation
• And of course a method to achieve what I want: To use the full 6TB without without this downloading scenario to the internal hard drive of my Mac mini M1.

BTW I use the Photos app only for very recent photographs as I store them on my external hard drive. I have no use for collaboration, sharing, albums and all that kind of stuff, so do not worry about that. In "Apps using iCloud > Photos is "On" I use an iPad for perusing and showing pictures and an iPhone for taking pictures during work

English is only my second language so I hope I explained everything in the right way .

Many thanks in advance for helping out!