Interesting question! I've never done those before, tho I'm from Finland so I'm not sure about the logistics (unless digital community copies are a thing). Still, I might look into it.
Here is a link from someone on itch explaining how to add them:
https://itch.io/jam/wretched-jam/topic/799347/how-to-add-community-copies
It is essentially setting a limited number of copies that can be claimed for free (or a reduced price) for people who might otherwise be unable to purchase them.
Many creators on itch set it up that for either every copy sold or whenever someone buys for above the suggested price, then the creator adds a free comunity copy to match that, like a person who can afford it would be buying their own and passing on a copy to the community, but sometimes creators just set some free copies to be claimed even without that, like a donation to the community, but only a limited number of copies.