A goal in Kanban?

Obviously not a Sprint goal, but some goal that gives focus to the teams.

Why not a Sprint Goal? Might they have a Sprint Goal that is flow-based? The optimization of flow under challenging circumstances may provide a coherent reason for them to work together.

First of all - take a look at the "Product Goal" that's part of the Scrum Guide 2020 revision. It might be relevant to what you're looking for. 

Additionally - a team using Kanban CAN consider using Scrum Sprints to help it focus and achieve effective cadence. Every Professional Kanban team needs to consider cadence as part of their definition of Workflow. Having a Sprint and therefore a Sprint Goal is one great way to have cadence...

If the team does NOT want to use cadence, then they still can have a "current goal" that they're focused on. Think similar to Sprint Goal but not constrained by the timebox of a Sprint. I've worked with teams that used this approach and it served them nicely. In retrospect, having the cadence of Sprints would have been even better for most of them though...

YMMV...

For me, Kanban strives to get an item across the board in the least amount of time possible without sacrificing quality or value.  Since most of the time those items are related to a deliverable of some kind why couldn't you adapt the Sprint Goal concept and craft a goal for each item to aid the team in focusing on what matters for that item?  The Sprint Goal helps focus on the work being done to build the increment of value for each Sprint.  An "Item Goal" could be used similarly. 

NOTE: I used the word "item" because I don't know what you call the things that you move across the board.  I didn't say story because User Stories is not a Kanban practice and Kanban was originally created to manage the process of manufacturing so I don't think they used User Stories either.  

For me, Kanban strives to get an item across the board in the least amount of time possible without sacrificing quality or value.

A nice description, but to build on this, perhaps consider whether this definition should refer to a constant flow of items, rather than a single item.

This is relevant, because one common practice is to introduce "expedite" lanes on kanban boards, which may provide opportunities to move an individual item across the board in less time, but often comes at great expense to the cycle time of all other items, and to the predictability of flow in general.