Why don't shared folders show up on the recipient's iCloud drive?

That was not helpful

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I’m concerned about how the recipient can access the shared folder.

• Participants need an Apple ID to view or edit files in a shared folder. If you invite someone without an Apple ID, they'll be prompted to create an Apple ID. Participants must click Add to iCloud Drive to open the shared folder on their device. 

If you have tried this and it doesn't work, you have not said so.

SirOmega wrote:

I shared a folder with someone who also has an iCloud account (using their email address they use to sign into iCloud). But with their iPhone and iCloud installed on their Windows PC, the shared folder doesn't show up on their devices.

Coming from a different product, I was used to having folders I shared with others show up in their account. So that they can easily access all the documents I put into that folder. Does iCloud file/folder sharing not work like that?

This is how iCloud Folder Sharing works.

https://support.apple.com/en-ca/HT210910