On an advanced roadmap plan a standard set of filters is available.
Is it possible to adjust or create new filters based on custom fields for example?
The server version of advanced roadmaps this is available.
Is or does anyone running or ran into the same issue and have anyone found or came up with a solution?
Or is Atlassian working on such a feature for the near future on Cloud?
On the cloud page you referenced there is a note about custom fields being able to be used as filters, assuming the field type matches the limited list. You can set up the custom field to be included in the list of filter fields under Configure > Custom Fields. On that screen there is a check box if you want the field to be included as a filter. Again, not all field types are supported, unfortunately. I don't see why something as basic as a user picker field is not supported...