Using Confluence Database, how to create a "board" view based on the "entry link" or "user"?

[Tim Haselaars]

I'm building a typical database, with per feature item:

- a customer relation stored in the "customers" databases

- a user (Confluence User)

I want to showcase a board where per lane, you can see the items linked to a "customer". Another view would be the features per "user".

When selecting the grouping for the "board" view, you can only select the regular database fields (like text, tags) but there is no option to group them by "user" or by "Entry backlink".